By the way, the "Hawaiian Waltz" is useless, Hawaiian music is always 4/4 timing.
Er, wait a moment. Try 'Pagan Love Song'.
Might not be true Hawaiian but let's be honest, a lot of music that people think of as Hawaiian really isn't. "Just for the tourists", as someone once told me!
Back on topic, I go the 'assembly route', too. I know many of the people who create the styles (and sounds, for that matter) in Yamaha keyboards. They use software that's not available to us, of course! But they are also superb musicians.
Let's assume for a moment that I waved a magic wand and gave all those people asking for 'real style creator' on the keyboard, and I'll assume that I also magically gave people all the
technical skills to use it. Now, how many of us would then have the
musical skills that my friends at Yamaha have? Composition, arranging, orchestration and so on? All absolutely vital. You have to think and play like a drummer, percussionist, guitarist(s), piano player, string section, horn section, plus all the soloists in the 'phrases'.
Do I have those skills? Most of them (but my guitar playing is rather ropey) and I created basic styles as far back as the 1980s! Would I be able to create a good style and be that 'pro-designer' now? Maybe, but I think I'd still leave it to my expert Yamaha friends! I think I'd stick to being 'pro assembler'. I remember back in the mid 1990s when we put that feature into a Kawai keyboard. Simpler by far than what we can do these days but I still managed to come up with some decent custom styles from those that my talented Japanese and American friends had created.