How would you change the mechanics for melee so it would require less dexterity to play but still keep it’s depth?
There’s a lot of ways you could potentially do that. For one, you could fix the bug where the last frame of jumpsquat won’t count in determining whether you fulljump or shorthop. You could allow Shorthops to be bound to a button instead of needing to release within the jumpsquat time. You could extend the valid dash range during dash dancing, add an extra frame of leniency to backdashing. Make it so jumping during normal turnaround still has you turned around. A lot of small input leniency changes that Project M made. You could make shield directly cancel into up smash or up B instead of needing to cancel through jumpsquat first. You could probably make L canceling automatic, and not lose that much (I just resent the idea that such a thing is totally pointless, especially when you have characters like ice climbers, who are very difficult to L cancel against, and who have a valid use for L cancel in the L cancel desync). You could add a small buffer period, like 2-3 frames. You could make Meteor Cancels mashable. You could remove the restriction on IASA frames to not allow dodges or B moves out of them.
And that’s about it. Beyond that, you’re changing the options the characters have or how difficult they are to perform in a way that affects game balance (due to strong options being too easy), or the distribution of options players will pick (due to certain options being over-centralizing).
The resulting game would still take a massive amount of dexterity to perform at, but you can’t really pare it down any more without giving something up about the identity of the game, in some ways this already is compromising some of the identity of the game.