Discussion about Sylvan (Wood Elves).

Well, I wouldn't say that. It forces the enemy to spend a turn to eliminate her, and even then, it's not always possible to reach her, only with ranged attacks. And if they manage to damage her, she'll "resurrect" after the battle, so no problem, let the enemies waste their time trying... ;)
As for the fact that it's difficult to upgrade her and she appears rarely, at least in my experience...