What if I tell my brother to take control of his life and leave his girlfriend?
Why would you want to interfere with their relationship?
He should realize she is holding him back and break up with her.
If it's true that she is bad for him then it's expected that you would have your brother's best interest. Explain to him why you think she is bad so he can understand your point of view. However, it's important not to be too controlling of your brother and to let him make his own decisions about who he wants to be with.
She's worthless and will hold him back from doing something with his life.
If she's truly negatively affecting his life, it would be best to explain your feelings to him. Just be sure to approach the subject gently and calmly because this is a sensitive subject. If he decides to refuse your advice, then you need to accept that and let him live his own life how he wants to.