Remember the overpresentation topic has a lot to do with the everyone theme for Smash 5, still. If we're in another regular Smash game where a lot of FE or Pokemon fighters are cut, at least it wouldn't bother for Nintendo to add a fighter to advertise their newest titles from those franchises.
Two arguments against Waluigi:
"He was only made to be Wario's partner!"
"He doesn't have moveset potential!"
First of all, play the spin-offs.
Well all characters fight alone, so their qualification doesn't rely on their partners. Plus Wario and Waluigi don't represent same series in Smash classification. In the case of Waluigi, his direct rivals are Mario, Browser and others, not Wario.
And it's been discussed a lot. Spinoffs are the basic references for all Mario main cast, so that all Mario fighters have for what Waluigi has at this point.
King K. Rool, before his confirmation:
"He's irrelevant, he hasn't been in a game in ten years!"
While I have been his supportor, I would not think this is an invalid point:
1) Such opinion could be from supportors of other characters from the same franchise, such as in DK series we have Dixie, Cranky and Pauline who are still making new appearances, and those characters sure do have what it takes to compete as well.
2) If we like the characters, what we should really concern is that why Nintendo don't volunteerly try to put the characters in more game but just keep them absent. In the case of KRool, fans are mad because he has been absent from many DK/Mario games that he could had easily fit in.
Irrelevancy can be
fixed, I think that's the positive attitude fans should take.