It's not just muscle memory reps ... it's clarity during points. I played with a guy that hit both 1hbh and 2hbh that were both 5.0 quality. He didn't seem to have much problem with technique mixing them in, but the "when" for each. He could hit quality topspin drives with both ... so both were always valid during a point. I think what he lost is that autopilot mode you need when playing your best tennis.
Since I am way past any competition that matters to me, I have the luxury of hitting what is most fun/satisfying. I have kept the flat 1hbh dtl (when in perfect strike zone) ... and 2hbh for everything else (that isn't a 1hbh slice or drop shot). That can be pretty autopilot ... only hit 1hbh when all the stars align.