And, after making my post, I had a better look through other Schticks in that Speciality, and discounted the 'affects foe schticks' option, as there's already a Schtick for that. Should have done more research before [strike]opening my mouth[/strike] typing!
(I'm running a three-player game in the contemporary juncture, where one of the players is a Magic Cop, so it's likely that many of their scenarios will involve an occult element, either in bridge or big finish scenes. And I'm running it outside Hong Kong, as the Magic Cop is immune to the home juncture Sorcery modifier, and I know London better. I appreciate that these are all extra issues that most may not encounter.)
Some of Basselope's suggestions won't work in the circumstances I'm thinking of, but that's mostly for reasons that they don't know, and I don't want to put up here as my players may be reading. [grin] As for several of the others, YOINK. (Which is the sound of them being added to the big bag of GM tricks.) Ta!
I don't want to just generally nerf Banishment, as the Magic Cop is initially notably lacking in any other alternatives other than 'pull out a gun and start blasting at the creature until it goes down', which seems a little bland.
I decided that, if the player agrees, I'll probably go with 'Banishment may, alternatively, cause the Foe to miss 3 shots'. Given that Banishment is also a three-shot action, that doesn't actually help the caster any, it just inserts a pause into the fight - but if they have allies, then it affords them the opportunity to get up to something useful. The other likely option is to inflict damage (like Blast, but limited to Supernatural Creatures, and costing Magic, so not as powerful/useful) - think the sprinkling of sanctified something onto a creature.
There was also the thinking that the Magic Cop doesn't really want to be causing creatures to flee into the city to cause more carnage - or do you all tend to go with a more 'terminal' effect of banishment, which causes the Creature to discorporate (as Basselope suggests), rather than just running away (as implied by Cheese It)?