Should I tell someone they are working too hard for their shitty job?
Why would you think you are in the position to say that?
Because they're wasting their talent and I know better than they do.
While it's great you're looking out for them, you shouldn't insult them like that. You don't know if they like they job and are happy with where they are. They don't need you to make them feel bad about where they are in life.
I didn't think this through, you are right.
You are very understanding, and I really appreciate that. It's just something I wouldn't do if I were you, because it will come off as being rude when you act like you know better. It's best to just let things play out naturally.