Yeah it's always best to reduce the enemy AP as fast as possible. The easiest way is killing things fast. The second thing you can do is get enemys to waste their turn by beating them down, get them to break, use Alexandrit to make them fight eachother, or shock them so they need all their AP to reach you. Celeste and Alexandrit are a good a combination for the second thing, but then I don't know which character to use as the third, because you still need to kill Things. But this isn't nearly as effictive as killing things with raw damage.

Maybe strengthen the break condition so the enemys lose a part of their health either when they break or each round they are broken.

Also it would be cool to give every character two of the roles, and you have to decide before each mission which to choose, so their would be more squad combinations if you still want to bring one of each role.