I actually hate the double tap for dashing as well, I'm glad that's not incorporated in this game.
Dashing with a shoulder button is a good idea; it's just not something you implement as a default when 99% of previous MMX games dashed with 'A'
I think an extra screen when you start the game that lets you pick between "Original" and "Modern" controls would've gone a long way.
I've been the type to always look at options before I start a game (started back in the PS2 era when subtitles would often be an option that wasn't on by default). So thankfully I was able to catch this before it became a problem for me. But I can easily see how others could falter.