Legato Scales. I will put up my speed to play a major scale as fast as any button player and match them, and I am NOT a pro, indeed, I now classify as being on the downside of my skills… lol
The advantage is all about being able to slip that thumb under the 4th finger and that the keys are right next to each other as opposed to switching rows necessitating more awkward hand positions… this gets even more amplified if they are a traditional 4 finger player.
Mind you, this is really reaching now, and individual skills play a big part but while at the conservatory all the piano players had an easier time than the button players in this aspect.