I wouldn't call Waluigi a complete meme. I mean there are only 2 characters left needed to complete the main Mario cast, those being Walugi and Toad. It's up for debate, but yeah, there are a lot of characters who are supported because of bandwagons, like Skull Kid, Shadow, and the characters you mentioned.
Remove
and replace them with those two and we have the complete mario cast.
Memes aside, and although PP is certainly iconic, it's a generic scrub. I'd gladly replace it with Waluigi.
Moving on
From previous posts: I've never seen "aggressive" behavior come from BWD supporters. Depending on how we define aggressive support for a character, I've seen fanatical posts, but nothing along the lines of hostile. I daresay that I've seen more hostile posts from other fanbases, but I won't point any fingers.
I also think that if we're going via a pre-2003 perspective, Marx is infinitely more qualified for being in the roster than BWD is simply for being more iconic to the series as whole and (arguably) more design space to work with.
In my opinion, for Kirby representation to be the best it can be without over-inflating the roster, these four fighters are needs:
1. BWD. The most popular Kirby choice, and represents modern Kirby best.
2. Marx. The most iconic villain from the series with tons of moveset potential.
3. Magolor. Very popular in Japan, and the face of Kirby's big comeback (think of it this way: RtDL is to Kirby as Awakening is to FE)
4. Adeline and Ribbon: Represent both the Dark Matter Trilogy and Kirby 64, plus lots of creative potential.