In most states that have addressed the question, it now appears that an accused whose defense lawyer is guilty of malpractice has to do two things: have the conviction reversed or vacated; and prove actual innocence.
Both must be shown. (Some states require one or the other only, or at least their courts haven't had to decide whether both are required. A small number of states don't require either.)
I can understand showing actual innocence. But there are many doctrinal impediments to vacating a conviction that have nothing to do with criminal culpability. Sometimes it may be close to impossible to accomplish. Not to mention costly. As a policy matter -- i.e. not a technical matter of collateral estoppel -- why should the plaintiff (former defendant) have to vacate or reverse the conviction?