They can only summon a few types of creature, I was just joking about how there's actually no technical restriction on a GM beating the people of TB, they just have to use GM powerz.
And it's easy to banish summon creatures. You cast KEL RA QWAN on them a few times.
I don't think this proposal has a chance at being implemented because you'd have to add a way of knowing which creatures were summoned and which weren't, put extra spells into the game and there's really not much point when the only summonable creatures that do damage are skeletons, mummies, ogres, bees and flies. We already have attack spells for disposing of those.