"The danger of having a good personality"... Ha... You could simplify your argument by saying an incompetent clinician can do harm and leave out the being well-liked (charismatic?) part. You could also easily argue that having no support at all (instead of incompetent support) could make a client's life worse and lead to suicide as well. BTW, do you have any sources to back up these claims that an incompetent antisocial clinician is better than
an incompetent pro-social clinician in terms of client outcomes ? Because you could also argue that grass is green...

Some people fit better with clinicians who are more "prickly" and direct, and others feel more comfortable with warm, charismatic people. It all depends. The relationship is the most important aspect of our work, otherwise everyone would go get therapy from a computer or a book. They come to therapy to have a real connection with another human being. Protocols, assessment and goal-setting is also very important, but secondary.