People are taking a cutscene whose sole purpose was to set up a basic plot of "save all these possessed characters" way too seriously. You need the most amount of characters to setup as enemies while also having the bare minimum of playable ones.
Kirby being the only one that survives is a ganeplay choice, not a story one.
And regardless of Sakubias, it HAD to be one of the O8, and, tbh, Kirby fits the role best out of any of them since this kind of **** is a monthly occurence to him.
Also, even from a story perspective, the initial cutscene is supposed to show the overwhelming power Galleem has. Some characters underestimate it and end up biting the bullet(Zelda, Mewtwo, Palutena, etc), others realize they can't do **** and try to run away but the beams are faster(Falcon, Falco, the Pits), some stand their ground but know they can't directly fight it but dodging ends up being futile(Lucario, Greninja, Link). And some are just straight up supposed to be comedic unless you believe Snake really thought that was his best option.
It's not stupposed to be a personal attack against your character who you believe to be OP. It's not even Sakurai showing how powerful his character is, Kirby only gets away because all the circumstances allowed him to. Had he hesitated in escaping, had he not possess a Warp Star or had the beams went into any other direction, he would be gone too: it was all luck.