at max level, i'd say no. reasons as follows
you're right, tanks need less stars as their utility is usually not hindered by star level, however
tanks need to take hits, 3 stars means a significant reduction in HP, armor (also attack but for tanks that's not really relevant). Also, at 3 stars, you can't get to g12, which usually provides a pretty healthy protection increase.
to me, at lower stars, this toon would mean he can take maybe 2 or 3 big hits less. that's usually enough to make a difference. But depending on your shard's situation, it might be feasible, easiest way to check is just to look at the top of your arena and see if anyone's running tanks of only g11. if they are, then maybe it'll work, if not, there's usually a good reason for it