Vulnerable as in are able to get in there and suicide bomb you unchecked. 2jt shots and 1 of anything else is enough to kill a t34 so unless it was cloaked when driving straight at the JT there wasn't sufficient support to counter the risk the Soviet was placing in their attack. Alternatively the ram came from a flank which is also fair game.
Imo Ram/off map is way too effective while relatively easy to pull even frontally (in 2vs2 games and 1vs1).
I would try moving redesigning Ram to be a skill shot that scale with veterancy.