At one time or another, every manager struggles with how to handle a weak employee. Perhaps she has adequate technical skills but lousy interpersonal skills. Perhaps he just doesn’t want to be there and creates a toxic environment complaining about everything that is awful about your company.
Make a decision. If the pros don’t measurably outweigh the cons, take action. Whatever you do, don’t drag it out.
This isn’t easy, especially when the person has positive attributes that everyone recognizes. But the damage caused by delaying the inevitable is bad for everyone: for the employee, for the co-workers, and for you.