Alan Dean Foster wrote a series called "The Damned" which explored this option as did David Weber (I think) with "The Excalibur Alternative".
(Massive Spoilers for fairly obscure science fiction stories below)
ADF's book wasn't much to my liking because I thought the protagonist was an idiot with no grasp of reality who remained a naïve one note character specifically to provide a counterpoint to the events of the book. The basic plot of "The Damned" was that humanity was as superhuman to aliens as we tend to think of as aliens being to us in science fiction. Basically while pretty smart, the aliens are generally smaller, weaker, etc... and see things even our weakest do easily as being superhuman feats. What's more the aliens are for the most part peaceful, as very few of them developed from predatory species (or otherwise developed on fairly idealic worlds) as a result when they get into an intergalactic war with what amounts to a multi-racial cult of harmony they don't want to join, it's basically galactic slap fighting for all intents and purposes, with only a few races being able to kill. When humans are discovered, being both physically powerful, and having predatory instincts, we're ultimately recruited and sent out to fight in this war in exchange for technology and being uplifted... and to put it bluntly as "the ultimate warrior race" we horrify everyone just by fighting wars more or less normally. This leads to some interesting problems where our allies ultimately start worrying about what happens when the war is over and all the aliens decide to go back to their peaceful little Utopia and leave all of these really dangerous humans now wandering the stars... which turns into predictable plots to kill us off or otherwise planetlock and contain us if I remember. It's been a very long time.
"The Excalibur Alternative" as in a similar vein, it's a spin off from David Drake's "Ranks Of Bronze" it involves a massive interstellar empire ruled by corporations that want to expand onto planets occupied by primitive natives and steal all of their stuff. Being very civilized however this empire won't allow more advanced races to terrorize less advanced species, while also wanting the resources, so their own way of getting around their thousands of year old rules is to basically fight proxy wars, where they find other primitive races to fight for them. So they go running around the galaxy and abducting primitive warriors, enslave them, and then turn them loose on various planets. Some of these aliens find earth and enslave a roman legion which they start carting around to conquer planets for them "within the law", leading another alien to show up to get one of his own only to find that in the "short" span of time humanity has progressed greatly, there are no more Roman legions, but we are in the middle ages with knights and this lovely weapon called the longbow. The aliens abduct an army of these guys and go around conquering different planets. After a few hundred years (scientifically enhanced lifespans) the knights manage to team up with some of the aliens that had also been enslaved, take over the ship, and pretty much head out into space to form their own empire.
The climax of this particular story involves the intergalactic empire realizing humanity is a threat, not only are we super-dangerous fighters (really strong, fast, and predatory) but are also hyper-creative compared to them and outright smarter, developing technology in the span of a few centuries that took them thousands of years, and realizing that as their society has also stagnated we're going to out advance them "quickly" in a couple more centuries. Their solution to this is of course genocide, while humanity is just barely developing it's first few in-system ships. On the eve of our execution at the hands of an alien Armada half a dozen ships decloak and pretty much wreck the entire fleet, turns out it's the knights and their new allies, after they escaped they started developing technology from the "base point" of the alien ship they took over and over a couple hundred years had improved on it greatly while the stagnant aliens hadn't. The knights now have their own little intergalactic coalition which had been hiding, their leader (still alive due to tech) is now basically the leader of this alliance, and they had been debating whether to intervene since there are now far more humans alive elsewhere than on earth, and the aliens control tens of thousands of worlds and their countless numbers where he has maybe five planets (despite the tech difference) but in the end decided to opt for "The Excalibur Alternative" and decided nobody was going to kill his homeworld after preying on his people for soldiers, and while it might be doomed due to simple numbers, he planned to make the entire galaxy burn for attempting this genocide and win or lose, forever more humanity would live on in the galaxy's nightmares....
I read both a long time ago, but conceptually both of them are huge "Humanity: Fuck yeah" concepts.
Warhammer 40k is another one (as others have mentioned). In Warhammer 40k the only reason why anything is a threat to humanity is because of the sequence of events that lead to the corruption of Horus and what amounts to a "long night" where a lot of technology like reliable FTL communications have been lost. In 40k despite a lack of anything resembling wide scale coordination, and with technology a lot of them don't even understand, humanity is fighting a war on like a hundred different fronts and managing to hold. The threats we see in the various "Codex" books are only supposed to be a sampling, the Imperium was made to be so huge and unstoppable in any real sense that they could theoretically introduce any number of enemy armies over the years as the market demanded. Chaos, The Tau, The Necrons, Hive Fleets, even Orks, individually none of it has a chance and fundamentally just picks away at the edges, and if The Imperium ever managed to restore some of it's tech, like FTL communication that didn't require increasingly insane telepaths, and could coordinate on a large scale, it would probably crush all of them combined like ants, even launching a crusade into The Eye that would finish what Horus was supposed to do before he went corrupt.
It should also be noted that some of the material for "Warhammer 40k" implies that humanity does indeed get it's act together and wipe out all of these threats (perhaps civilizing and allying with some of them). A few of the books and such have involved stamps implying they were ancient records from "the dark ages" being looked back on from some far future generation learning about history and the horrors of this period... which implies that despite the pre-amble
in the end it wasn't hopeless at all.
As I said, Warhammer 40k relies on ideas like unreliable communications, information hoarding by various factions, inter-factional fighting, and similar things, and despite that The Imperium is still the central force of the universe, again, stop and think about what it would mean if all of that stopped and you wound up with The Imperium acting with large scale knowledge and coordination, with hoarded tech knowledge being circulated and innovation again taking place. There are some science fiction empires that could potentially handle this (throughout the scope of sci-fi) but not many, I mean at it's height The Imperium apparently had singularity technology as they both have warheads that deliver black holes, and I seem to remember at one point reading how one Chapter Artifact was a spear that has stabilized singularity blades (ie basically a blade shaped black hole on the end of a generation pole). Just imagine if the Imperium regained that kind of tech from the recovered archao-tech and archives, even the bloody Necrons would cower in fear realizing their own inferiority.
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Speaking for myself I tend not think of humanity as being all that warlike despite my nihilistic rants. I think a lot of our problems come from too few resources, too many people, and being divided into too many nations and cultures. If we were ever unified into a single nation/culture and kept our population in line with the resources to maintain a high standard of living, I think we'd actually be a fairly peaceful people. As a general rule those who like to kill for the sake of killing and revel in real violence for the sake of violence represent a minority. The simple reaction to some of my posts at times (backed by hard facts and logic) and the way people fight against it sort of makes my point on a lot of levels oddly enough. Despite all the wars and such on Earth (which have come from the things I mention) I could easily see us as a bunch of intergalactic pacifists, and truthfully I'd imagine if we ever became a powerful race, and wars broke our elsewhere, our instincts would actually tend towards isolationism.
Interestingly Larry Niven wrote a huge series of books and short stories called "The Man - Kzin Wars" the premise of which is humanity more or less unifies earth, gives up violence, and is peacefully living in it's own little pacifist utopia. Eventually this race of predatory cat-men that is running around conquering the galaxy finds earth and starts trying to prey on us (starting with stories like how a human captain in an unarmed ship weaponizes his engines despite his instincts when pushed far enough). When the threat becomes known, despite some initial opposition due to all of our work, humanity again arms itself for war, and let's loose all that pent up aggression and warrior instinct we had once reserved for each other on the "poor kitties", leading to epic space warfare between the "Hairless Monkey Boys" and the Furballs". The Kzin being continually surprised at the ferocity of humanity in part because when we were 'discovered' we were basically living as pacifist space hippies (however it's important to note humanity and it's sphere of influence was not low-tech compared to the Kzin, we just hadn't been using that tech for war before that point, so it wasn't like there was a massive increase in tech base in these stories, and indeed the subject of some early ones had to do with humanity building up it's military-industrial complex and re-tooling things for space war... a sort of slumbering juggernaut that wasn't seen as a threat due to the racial demeanor more than anything). You might even say "Man Kzin Wars" was the very first really "Humanity Fuck Yeah!" sci-fi series that took a really "Humans are awesome" view as opposed to portraying a galaxy where even if we're somehow numerous and dominant, we ultimately come up lacking compared to most aliens and their cultures on a small scale.
