Life steal is only worth it if you can deal a lot of damage while its active. It works well against animals and pets because they dont parry.
If you use it against a player, and then he just sits there and parries all your hits until Life Steal is over, then its kind of worthless. If you dont do damage, you dont get hraled.
This is the problem of using it in large fights. It has a very recognizable yell, so enemies can tell that you are using it. All they have to do is parry and you dont get much life steal.