For 15 more fuel Churchill gets 1400 HP, support abilities, plus it's a non-doc and has better gun and MG.
On the other hand KV1 has better armor (240 - 270 is rather irrelevant difference), speed which also irrelevant for a damage sponge unit - it's not like you will flank anything with 5.1.
There is not a single point why KV1 should be way worse damage sponge than Churchill if they are priced almost excatly the same in terms of tech and unit itself.
spedd is revelant while running away , church has smoke cause they dont have a mobile mortar to give them , 30 armor is a lot (ex. ost p4 cost 25 less than okw p4 for 50 armor that can be gain back at vet 2, and okw has a bit worse stats too) and they get 0.8 damage modifier ,alvin locks you out of comet and the gun is almost the same (see stats i linked)