D&D Shape Change Vs. Time Stop?

[Souplex]

Also unclear to me is whether you need to concentrate to keep outsiders banished, or if you can free your concentration up for other things.

I was told that the banishment was the concentration.

While yes, the banishment in general is concentration, I'm referring specifically to outsiders. (In D&D terms Outsiders are being not native to the Material Plane)
"If the target is native to a different plane of existence than the on you're on, the target disappears, returning to its home plane.
If the target is native to the plane you're on, the creature vanishes into a harmless demiplane. While there, the target is incapacitated. It remains there until the spell ends, at which point the target reappears in the space it left"
Basically I'm not sure if the second bold'd section applies to the the whole thing, or just the part for locals.
https://www.dnd-spells.com/spell/banishing-smite

Also, what about the other points I added to that post?

For choosing between Spirit Guardians and Swift Quiver: Do you find yourself in situations where you have multiple foes within 15 feet, and are comfortable staying that close? If so take spirit guardians.
Do you find yourself with uses for your bonus action more useful than 2 heavy crossbow shots on most turns? If not take swift quiver.
really, at a certain point it comes down to play-style. You're a while off, see how your GM runs things. If they love swarming you with Melee mobs or you develop a fondness for melee combat, spirit guardians increases in value.
If they love ranged foes or bosses, swift quiver increases in value.
Observe how you play, and what kind of game you're in. I can only give broad advice.

 

[The Wykydtron]

I've always wanted to make Time Stop less niche/more impactful without making it ridiculously overpowered and just plain unfair (3.5 player here, off the top of my head, the only way I think you can do damage conventionally with Time Stop is Delayed Fireball detonating as the effect ends) but just as with Jojo, time stop effects are quite impossible to balance, especially when in DND you don't have the luxury of being Araki plotholing and asspulling his way through everything as per usual and everyone is used to it. Anyone remember Star Finger? Yeah I think Araki would like for us all to forget about Star Finger.

You give a PC the ability to deal damage in stopped time he'll abuse it whenever he can and your campaign will go off the rails quickly and if I as a DM give a villain the ability to do damage in stopped time it's at the least unfair to the players (especially if one person gets Kakyoin'd right of the bat) unless you pretty much tell them beforehand he can stop time, and stop time better than regular Time Stop. Then you'll have hours long planning sessions of how they can OTK this guy without him even noticing them, which just means he can't even use his cool ability to begin with.

Still, Time Stop is a 9th level spell and getting Kakyoin'd is basically a less effective way of being instakilled by Finger of Fun or Power Word: Skill so in that context it might be ok to just buff Time Stop and give the guy a story reason why.