I like the concept here, but certain champion affixes are creating significant issues in mob farms, plus the enchanted book spam is less than ideal in a farm.

Being able to block champion spawns from spawners would be greatly appreciated.

I was mainly referring to vanilla spawners. Changing the event from join world to SpecialSpawn (and checking if a spawner made the entity) was successfully able to block them from showing up in spawners

Are you talking about just vanilla spawners or maybe some other methods as well?

I haven't received any champions from spawners in my testing worlds, weird.