That Great Yamaha sound is no greater that great Korg sound, or Ketron sound ... or that great Roland sound. Wersi and Gem are the only 2 that never lit my fire in the expensive lineup. I ever prefer Casio to those 2, but the top 3 are easily usable on most stages with terrific success.
I'd bet that NO one picks Yamaha over Korg or vice versa for sound ... it's features and OS that separate the pack. They all sound great.