There have been several justices that appeared to be ideal only to turn out bad - Earl Warren is the prime example. A Justice is a lot like a mutual fund with the disclaimer that past performance is no guarantee of future success. Once he is seated, he’s set for life and under no control.
Democrats haven’t had a justice turn conservative since Whizzer White under John Kennedy. Republicans got Warren, Brennan, Blackmun, Stevens, Souter, Roberts, O’Connor, Kennedy, Potter Stewart, and a few others. That’s a lot of misses by one side with so much at stake.