You are talking about button bloat there, which is not really an accessibility issue (unless you are talking actual disabilities preventing you from using all keys/buttons). Condensing long combos where you need to stay aware of what exact step you are currently on only makes them more difficult to play by taking a ton of muscle memory and peripheral vision out of the equation. For something like Reaper, sure why not. It doesn't matter since it's just a 1-2-3 combo with literally zero distinct interaction with your kit.

But pressing 1-1-1 doesn't actually make the job easier than 1-2-3, you aren't going to forget to use your 1-2-3. You aren't going to miss any cooldowns because your eyes get information overflow from the 1-2-3 buttons (at least after a few days of playing any melee job). And for jobs where it actually matters which was the last combo action you took, it's just an active hindrance. You need more focus on counting your hits than knowing where your finger is at, or identifying symbols than knowing where the blinking light is.