It's damage is a little ridiculous, but there's literally only one doctrine with it, and it's pretty obvious when your opponent is using it...
The old Tiger Ace was in literally only one doctrine and it was obvious when your opponent was using it... thus it was balanced.
An OP unit is going to be OP no matter in how many docs it is.
If you are having your tanks one shotted across the map, given the amazing B-4 turn speed and shell travel time, well, you might want to consider not sitting with your tanks being immobile for extended periods of time against B-4 user.
You can´t repair while moving your tanks around... good players will just wait until you repair (you can hear that through the fog of war, or someone uses a recon) or not fire the gun at all to make you nervous about repairing. Thus once a B4 is on the field repairing is way too risky. Versus good opponents its even impossible.