"That's because a big roster"
Well, no. I already explained how something like SSE could have been improved significantly without changing the roster size whatsoever.
(In principle they could even bring back something like character-specific Break the Targets by just focusing on it for select members of the roster instead of trying to be inclusive of all ~60 characters. Maybe just do it for whoever the respective newcomers in that game are or something.)
"Do you mean the notes they put at the end of matches."
Bonuses. Both in the singleplayer modes as well as in the multiplayer matches.
"I think Pokemons have become bothersome,"
All items are bothersome and imbalanced. Having ten Pokemon from different players on screen at once in Melee is one of the more hilarious interactions one can have in an items-on match.
"In regards to making it more like Melee, besides Sakurai's vision. I could see that level of speed and gravity coming back, but the wave dashing I'm not so sure, since in interviews it seems like it was something the developers knew it was there, but never capitalized on it."
Not capitalizing on moves like that were why they worked so well. It was something that was there if someone wanted to learn some techniques with more slightly more advanced execution reqs, but players could win matches even without knowing it existed. Sakurai had this nightmare scenario of pro wave-dashers griefing Smash newcomers, but none of those moves were even a quarter as advantageous to players as something like Brawl-era Meta-Knight was.
"I'll be down if they took their own vision to Smash's version of Nintendo IPs, not taking assets from other games"
I am fine with Smash taking assets from other games -- especially when the alternative is like SSE where 90% of the enemies were ugly OC-looking nobodies who have never been in any Nintendo game before or since.