the HP is the only way to make churchills durable against axis late game without giving it elefant/JT level of armour because of the way pen works. the churhill is pretty much fine as is; certainly durability wise.
If churchill is fine as it is, then we should agree to limit this tank as one per player at a time. Of course same thing for the KT - this is a problem that wasn't solved yet.
For instance, I don't think there is comparison between a Tiger and Churchill in terms of durability, and that is kinda screwed up both reality and balance wise. You simply cannot adventure into enemy lines with a regular Tiger and not fear to lose it while you can do this with a churchill with almost no problemo.
I think the problem is related to heavies in general and not to particular call-in units. The spam of units that are good at all, can take alot of punishement while inflicting a ton of damage should be forbidden.