So what would the total spawn rate be on hard/elite after the reduction? Initially, you said it was set to 10%... it's pretty obvious that its more than that now.
I think the damage boosts should be dropped down 40%. This would put their damage output close to red named end boss damage. (It's stupid to have trash mobs hit harder than bosses.)
Hirelings are getting absolutely slaughtered by Champions. I'm glad this is on your fix for a later update. (please include summon monsters and wolf pets / iron companions)
Please do not add more champion immunities like FoM. It's been a lot of fun playing with groups using tactics like pulling into dancing balls and webs. Please don't take away group tactics with crowd control immunities.
I would also add a way for the Champion buffs to be dispelled. If a Wiz wants to spend the spell points to Greater Dispel, Energy Drain, then cast an insta-death spell, this should be another viable tactic.
I think overall the changes look good.