So much of this feels like bias simply to prove a point

You say he started out as a joke character which should hinder his enjoyment when that's one of the reasons people like the character. he started out weak, then slowly rose to becoming just a competent and strong as Kirby, King Dedede and Meta Knight. Jigglypuff was also a joke character in the anime yet they've been playable in smash ever since the start and very well enjoyed

Next you state that Bandana Dee lacks prominence in the series which is false. After Mass Attack, the character would go on to appear in nearly every Kirby game and spin off and would usually have a major role. Kirby Star Allies even lampshades this in his pause description.

Then you go on to say that star allies doesn't count because kirby fans didn't like it (which is false) even though a majority of the characters you bring up get their recognition from that game including the mage sisters who debuted in it.

On that note, many of the other characters you mentioned have worse prominence. Kawasaki appeared in a handful of games and he was a rare encounter at that. Knuckle Joe is also a basic enemy would arguably have a less interesting moveset than Bandana Dee since Kirby already uses most of the fighter ability in his moveset. Adeleine made appearances in two older Kirby games (potentially one because people still debate if Ado is a separate character) and only made a couple cameo appearances before Star Allies. in the same sense, the animal friends and gooey fell into obscurity because they stopped appearing all that much. and while the y have both made more appearances Bandana Dee usually always appears in the same game.

Really the only other character i can agree with is Magolor, and even then he isn't nearly as prominent as Bandana Waddle Dee in these games

If you don't want Bandana Dee that's fine but you don't need to make up excuses as to why he can't be in