I don't know about you, but honestly I have not had a single problem with a Bowser in the 500+ games I have played so far, and he is one of the most common people I have played. I think he is overhyped because he hits hard, and he has more speed than most heavies, and people don't have much experience in the game, but honestly, his moves are predictable and punishable, and he will probably end up falling to mid- high tier or the low end of high tier.
And Rosaluma is not OP. People just don't know how to face her yet (She will probably still be high tier though).
As for Bowser Jr. No. He is just not high tier. He is probably low tier seriously. Every time I see Bowser Junior, I just go in no matter what character I am using because of how bad he is.
Additionally, you forgot entirely about:
and
at the very least and
and
and
and
.
I won't make an argument against Ness, but I really don't think that Villager is a problem either.