Of course, it's completely impossible that any of that design was created that way for gameplay purposes. Because, you know, it totally wouldn't make any kind of sense for an enemy force with several levels of strength (which is incidentally more interesting to play against) to make each of their types instantly recognizable even in the midst of frenetic combat. Except that it would, and it would require that each enemy type look, sound, and move in extremely different ways, so that the player could say things like "Aha, I can see that this enemy is a grunt, and therefore little threat. I will instead focus my attention on the hunter, who is much more dangerous and likely to kill me." The ability to make judgements of that kind is vital to gameplay and has been around since people started to notice that the mushroom and the turtle did different things if you jumped on them.
Furthermore, it is clearly nonsensical that the spartans (sorry, SPARTANs) all look the same because they grew out of a design for a single character. Master chief needed to do two things design-wise:
1) He needed to look more powerful than a regular human. Thats easy, he's in power armor. The beckground stuff exists to make the player feel empowered and explain that whole "protagonist invicibility" stuff and gameplay mechanics like the shields.
2) As the protagonist of a first person shooter, he needed to be relatively faceless so that the player could more easily project onto him. This has been a consistent design element throughout the history of FPSs and exists because a first-person viewpoint is the most immersive.
"Oh wait, shit" says Bungee. "Now that we've branded such a successful character based around those two principles, we suddenly have to make a game where there's tons of those guys? I guess we'd better diversify their appearance a bit. Except wait, we can't make them crazy different, because A: that would ruin the instantly recognizable 'this is a spartan' branding we have, and B: could potentially confuse players in the midst of the game. In the middle of a hectic firefight a player has to be able to instantly tell the difference between friend and foe, especially since we've made a game so unforgiving that a split second hesitation could mean the difference between getting a beamsword shoved up your ass or not."
Also, its squad-based. Which basically just reinforces everything I just said. Now to balance out my unusually reasonable internet argument - Bob, you're a massive fucking toolbag, and I'm pretty sure they gave you a second, more controversial video is because you troll well enough to significantly increase siteviews. Which I guess is working, so congratulations. Hopefully this means your movie reviews will be a bit less ranty and stupid now and more like the informative ones you used to do.