I actually think this spell, and this issue, sits at a very important structural point in terms of making the game easy or fun for players, for the reason that Banishment is not really a great spell to use on players. It's a dick move.
Wow, I'm in total disagreement with you here. If it's within the enemy's capabilities and it's the logical move, it's
never a "dick move" to use their abilities in a tactically sound way. In fact, I'll go so far as to say that it's doing your players a disservice to softball things, including things like this.
First of all, it removes a player from the action for the duration of a combat, possibly hours of play time ("Sorry, Jerry, hey, while you're out, want to make a quick pizza run?") and secondly, targeted at the right PC (*cough* the Cleric of Life *cough*) in a tough fight, it has the very real potential to be an uncounterable win button.
If removing one specific pc from the field is an "uncounterable win button", then there is a problem far worse than a single spell here.
I flatly disagree that it's an "uncounterable win button" for a bunch of reasons- not least because no one pc's removal, via
banishment, sleep, hold person, power word kill or what have you, is EVER an "uncounterable win button" (at least in my campaign)- that implies that the loss of (f'rinstance) the cleric of life leads to an automatic TPK. Never seen it, ever, in 34 years of gaming.
I may not like players, but even I recognize that this combo doesn't just make life hard for them, it breaks the dynamic of the game.
Nope, I don't buy that either. There are often times when, for any number of reasons, one player or another has to sit the game out for a while: they're dead, they're sick or otherwise can't make it to the session, his or her character isn't with the rest of the party, is paralyzed, etc.
And don't forget,
banishment is a concentration spell. There are built-in counters to that- break the caster's concentration!
Making Banishment challenging serves /everyone/.
Here, on the other hand, I absolutely agree with you- with the caveat that I mean "the material component part of banishment should be something you need to have, not subbing in an arcane focus or component pouch". To my mind, determining what the material component for a particular enemy ought to be is a fun challenge in itself. (Or it can, and I will go ahead and say should, be.)