Ok so ze has come far and all but a few other suggestions I have in mind.
Zombies:
Scout speedbuff should also reduce knockback. Not a lot of zombie scouts due to speedbuff being ruined by 10 heavies.
Soldier: fine
Pyro: amp up the damage a bit on the explosion or make it so humans are also effect by gas as well of the current fire damage
Demoman: Charge is nice however due to knockback makes it useless. Make demonan explode, otherwise no use as a zombie as we can't even trimp
Heavy: freeze effect damages enemies
Engineer: auto disable ubers by draining the medics while also disabling buildings
Sniper: piss
Medic: health sapped goes to nearby zombies as well (like an amputaor)
Spy: Good as is
Overall changes:
Things to disable or change:
heavy minigun knockback overtime reduce - make it so heavy minigun stops doing knockback to zombies after 40 rounds have been shot.
Or
Heavy minigun overheat - uses up more ammo and can not be replenished when shooting.
Scout: sandman, wrap assassin, cleaver: stuns zombies on impact
Medic:
kritzkreg : disable - useless
Vacicator: disable - useless
Quickfix: slow down healing but a bit above normal medigun and jack up uber to be aoe (simular to amputator)
Stock: increase uber regen to the speed of the kritzkreg