I’m going to be honest with you,
Bandanna Dee looks pretty plain compared to some of the other Kirby characters.
Basically when Bandanna Dee was first created and used, it was literally just a Waddle Dee with a Bandanna as a Joke boss.
They later gave Bandanna Dee a spear and a playable character in Return to Dream Land because they needed a 4th playable character. However, after that Bandanna Dee wasn’t given a major role until Kirby’s Rainbow Curse? from the Wii U because they needed another playable character, and there can even be 3 of him playable at once. Before and even after that, Bandana Dee consisted of appearing as cameos or just as an assisting NPC.
By the time Kirby Star Allies came upon, Bandana Dee was already popular and had enough plot significance to be friends with Lirby that he is now considered to be part of the main Kirby gang.
To be honest I’m overall neutral on this, but back in 2015-2016 Bandana Dee was practically everywhere in terms of appearances, from playable character to just an NPC. Luckily for Bandana Dee, he was popular enough to be part of the main crew by the time Star Allies was in development.
Aside from that at least he has a spear, which at least makes him stand out.
Also, please compare Bandana Dee to Captain Toad, they the both most comparable comparison, being generic characters turned into unique characters.