Well I was not trying to be realistic, it was just my ideal roster.
Anyway, in that case:
(Ganon)
(New gen rep.)
(New IP, maybe someone from Arms)
(Nintendo Labo WTF character)
I can't cut more than this, the remaining ones are all important and I want to keep some newcomers to give the game some "new" factor. Any other cut and the roster would feel dull, old and very disappointing for a new game.
The only ones I could cut are Mewtwo and Pit, but Pokèmon is a big franchise and Pit is the only NES rep. remaining.
There are 2 versions of Ganon, but I can't cut any of them, Ganon is important in some games and Ganondorf is important in some others; they are the same entity but they are equally important.
I even had to cut Wario against my will, and every DK side character as well (because Yoshi and DK are branches on Mario and can be still considered as Mario characters).
I probably could cut Ness though I decided to keep him because he's one of the originals... but I had no mercy for Jiggly, Mewtwo is way more iconic and important.
As for the newcomers:
Ganon is the bad*** newcomer to build hype
New gen Pokèmon rep makes sense and it's needed IMO
New IP to keep the game fresh and up to date
Nintendo Labo as WTF character because we need something unexpected and iconic to give the game an identity (a robot made of cardboard would work just fine).