I would suggest, for my part, making the summonings into Diminishing Returns.
For example, say a wererat summons 2d4+4 rats (I don't know the number; I literally pulled that out of my ass). Every time it summons, reduce the roll by a -1. So the next time it would summon 2d4+3. Then 2d4+2. And so on down. Eventually, it'd be summoning something like 2d4-10, and will be getting only miniscule, or zero creatures for summon.
This would still allow for high numbers of summoning creatures at the start (I feel there *should* be), but the tediousness will go down, and make them easier to kill.
Obviously the numbers hree are very tentative. But it gives you an idea of the sort of thing I'm wanting to suggest. Maybe lowering it faster, or slower.