The game doesn't have to play like Melee. Simply allowing dashes to be cancelled is a start towards more offensive options, and that's a simple thing because Bowser can already do it (for whatever reason).
And you speak as if Sakurai isn't tweaking thousands of variables every day already. That's what testing and polishing a game entails.
All I'm saying is for the game to 'feel' like melee changing the speed will not do much. You have to change air speed, height, etc. Landing speed, dashing speed, turnaround speed, and a bunch of other physics things.
While he is tweaking numbers, he's not setting them to polar opposites or anything radically different. I'm sure there's a variable for 'air_dodge_directional_velocity' which is currently set to zero, where in melee it might have had some number set to it. Things like that are likely not going to be changed because it could change the whole flow of the game. It's more like he's changing 'knockback_distance_bowser_fsmash' from 18 to 18.5 or something. It's more complicated than that, i'm sure, but he's still tweaking, not implementing alternative physics that could potentially break the game.
Marvel 3 does it is with X-Factor just fine. Totally doable.
X factor changes speed/damage, etc, right? It doesn't make the game play like
Changing speed will never ever ever ever ever make smash 4 'feel like melee.' You have to change WAY more than that to make this feel like melee.