It's not only a HP advantage, it's the double amount of HP, its more hp than any heavy has, you need a lot of resources to counter this HP pool. Also the grenade ability wipes paks and the non doc smoke provides further utility. Its definitely worth 170.
eh, it's a lot of health but almost everything will always pen. it does take a fair bit of resources to counter but the same is true of the VI/VI B/ISU-152/IS-2. they all cost quite a bit more but they also all have quite a bit more going for them than hp.
the nade is strong but i would consider blitz stronger and other abilities (secure mode

) weaker. afaik relic doesn't factor the vet abilities into the units cost and they've been very uneven in the abilities implementation, particularly among the vanilla factions that they were starved for time with. the nade will wipe infantry but you can move away from it or retreat and with the churchill speed you can see it coming. one pak isn't going to counter the churchill but it doesn't counter any of the other generalist heavies either.
the smoke is a good ability but it doesn't have much utility for the churchill itself, although you can spin the tank around and turn it on if you really want.
i guess what i'm saying is, i don't think the churchill is as good as a comet and while i don't think 170 fuel would be the end of the world, i think 160 or 165 would be better since the churchill should be used along side fireflies which are 155 fuel (regardless of their cost effectiveness, they're expensive).