The thing with m10s is, nerf their speed and they become worthless, remove human crush and like mysthalin said, they get clogged up, its an extremely hard unit to balance in EIRR
Give it seperate buffs then to make it easy. Veterancy should be able to do this, give it completely offensive buffs and keep the doctrine buffs.
eg. Vet1: Accuracy 1.15 (instead of received damage 0.85)
Vet2: Penetration 1.15, Moving Ability (moving accuracy penalty removed) (the moving ability replaces Acceleration 1.2)
Vet3: Damage 1.2 Penetration 1.2 (keep the same)
This should help a lot, instead of imitating 588 health or so at vet1 stacked with the +25% health ability, it stays at 500 only, and at vet2 it won't be nearly as super fast, it will just have a slightly better chance of killing infantry the normal way.