[Snake]

FP drain is very unreliable, I'd probably just go with Collector's own idea and make it so they get unsummoned on the next round due to "lack of Focus".

Another wild idea would make it so Summoner (Base Class) has an innate that, upon defeat, they recover 2% of their maximum HP/FP while unsummoning each of their active Youkai and putting them on a permanent (or lenghty 5 round) lockdown.

Priest's Shine Knights can afford staying since they're a one-time deal after a massive invocation and only limited to 2 at a time, but I think their Total Control should be disabled so they become dumb and berserking while the Priest is out cold.

Engineer Bots should stay as they are, since it's in their gameplay (Medicopter) to actually save the day by stalling anyway. Plus, they don't have the same potency as a dang Suzaku or Seiryuu.
Don't cost as little to be put out, as in can't be active more than 1 at a time to a maximum of 4, and a total of 200 FP cost vs a Summoner's 5+.

Honestly, you'd only ever be finished off by a Railgan if you're too far away form it, you'd only ever be finished off by a Turret if you're a donkey, you'd never be finished off by Metalaegis and Medicopter's peashooters that never got rebalanced with the updates to scaling. Case closed there, lmao.