I think the Guard Dog will overthrow TF2's balance as a playable class.
"Guard dog release! OMG LULZ asDFGH"
Servers full of only Dogs.
How does one headshot a dog, damnit? Makes my rifle useless.
As an engineer "Buildable", whereas, his dispenser and sentry are replaced with a "Dog House" that spawns dogs every minute after one dies, yes.
That is balanced.