Why don't just make it more expensive and revert the popcap change, in the case of the Churchill. I'll say it again, i think it's gonna be easier to balance both the Churchill and the Comet if we treat them as a single other heavies, with only 1 been able to field on board.
If you nerf by 400HP the Churchill, you will basically have to reduce the cost which would still lead to spamming them in order to be effective.
I'm again limit Churchill to 1. Brit dont need a KT clone.