Don't perticularly care what it was DESIGNED TO DO, what matters is what it SHOULD do. What it should do is guarantee engine damage and that is it. From there you can combo with flanks, il2 bombs, typhoon strafe, I really don't care. But it'd be a lot better if it wasn't such an RNG roll.
I don't see why it should be an RNG roll either. There's tactical strategy to discarding a tank inorder to combo. It shouldn't be a "oh shit, tank gonna die" button.
I played the game when it was a reliable way to disable a tank, granted it REALLY disabled a tank, but still.
Right now it's scaled with armour because of the pen value. It's less likely to disable heavy armour. Guaranteed engine damage on something like a KT or would be batshit broken and well worth the cost.
Even right now, if you know the tank is going to die you can use it as a guaranteed 160 damage and maybe bonus crits. We don't want ram to be a sure fire way to disable much more expensive armour, certainly not when you also consider things like the very prominent AT satchel and incredibly potent Su85.
Its fine as it is now, guaranteed engine damage would absolutely break the ability.