All skills have their use, but picking skills for the wrong reasons or with the wrong setup make them useless.
Aiming for serious injuries is useful if YOU can create them, and not hope to get lucky and find an opponent injured by someone else. Most glads do not have auto heal, you are simply overestimating how many glads will get seriously injured, and out of that how many are willing to leave their injuries on indefinitely just for you.
If you can't create any serious injuries yourself, then it's not the skill's fault you can't use it enough.