I'm not a Kirby fan so I may be missing out on something, but honestly a generic Waddle Dee sounds way more enticing as a newcomer than Bandanna Waddle Dee - they have bows, axes, balloons, swing ropes, missile launchers, cars, snowballs and parasols - why limit them to just a spear?
But more importantly those 2 characters are also first party. And nintendo can do whatever they want with those. But if it's 3rd party, then it really needs to stick to the video game characters only rule, whether for costumes, or actually playable.
But...this is also sakurai and he's shown time and time again that he'll do w/e the hell he wants, so if Spongebob, Shrek, Goku, or any other meme non-video game character got in, there's not much any of us could ever do about it anyway.
...
You know what? so long as Geno Gets in I really don't care anymore tbh...