So as I see it, this only levels the playing field and gives you a small chance where you wouldn't have any.
Are you kidding? You can definitely play the game without using Leech at all. In fact, if you don't want to be ridiculously overpowered you HAVE to skip leech.
You can heal a character with a high fire resistance by casting fireball on him too.
Game is shit I guess.
Now imagine that you didn't have to stack fire resist. Imagine there was just a talent that gave you +100% fire resist.
Now imagine that about two thirds of the enemies in the game deal nothing but fire damage.
That's what Leech is like.