I think it's worth noting that in Kirby Fighters 2, there's five non-Kirby fighters. As you'd expect, there's Bandana Dee, Meta Knight, and King Dedede, the most prominent characters since Return to Dreamland. There's Magolor, who had only been playable once before at that point, but still makes frequent appearances in a supporting role, would later get an extra mode to himself in RtDL DX, and is arguably the next most important character after the main quartet. And the last one? Gooey, who had two appearances early on, vaporized from the franchise for over two decades, and only came back as part of the big 25th anniversary ensemble in Star Allies.
Also worth consideration is the unlock order. Bandana Dee is already unlocked when you first boot up the game, Meta Knight and Dedede have to be unlocked by playing the story mode, and Magolor's unlocked at Rank 39, pretty far into the game. Gooey is actually one of your first unlocks, at Rank 3. Now, Gooey hasn't had much appearances since then, but it's still interesting that he out of all characters is placed so prominently in the roster.