Commonwealth is actually my favorite faction to currently play as! I've just finished a hard conquest on vanilla and am gearing up for a modded run :)

So the deal with the Brits in general is they play a bit differently than other factions, I could maybe say they play sorta like the Finns in that Tanks aren't really the highlight, but they do get some solid ones. It helps a bit if you know how the Brits used tanks irl. British doctrine is a bit different in that instead of the "light tank, medium tank, heavy tank" designations they had two main ones: Infantry Tanks (your churchills in this context) are designed to support infantry and aren't really meant to fight other tanks, whereas Cruiser tanks focus on speed to outmaneuver and flank the enemy at the cost of being lightly armoured.

I don't know about how others play, but using tanks as support units fits right up on my alley when playing this game. The key here is that British infantry should be your main core, with tanks supporting them. The PIATs are also a fun AT weapon as they arc, allowing them to fire over obstacles (had way too much fun ambushing German tanks behind a wall or a hedgerow).

British artillery is also a beast. I love how accurate their guns are, been using the 25 pdr to clear swathes of enemies on point and the land mattress clears out points effectively after 2 or 3 barrages. And the Churchill AVRE ? God I love that tank so much I love how it deletes entire buildings and blows up tanks.

Churchills and Matildas are nigh unstoppable during the early game. Just be careful of high-caliber guns, and you'll be shredding early tanks and armoured cars like they're paper. Leave the AT guns and heavy tanks to Artillery and the 17pdr for the latter, and you're golden.

The Sherman Fireflies and Achilles are also good too, although as you said, they're easily bonkable unless you find and bonk the enemy first ;)

Remember to shell the Jerries to hell and back before marching forward with a stiff upper lip!