Kirby's survived far worse.
Like being thrown into a dimension of pain.
In addition, he would, if he swallowed Buu, gained Buu's powers, whatever they might be, and more.
If you can do a little bit of fencing and Kirby eats you, he becomes one of the galaxy's fiercest duelers, firing lasers from his blade and eviscerating all.
Even if Buu wasn't digestible, he can simply eat something else like a torch or a tree for a nifty ability.
To top it all off, his strongest attacks, such as summoning the Star Chariot, a super ability, hypernova, they all have destroyed countless abominations!
The Star Chariot was used to destroy Nova, the wish granting construct so large the sun and moon had to team up to keep it from smashing Pop Star into star dust, he destroyed the eldritch abomination Marx and his soul, after Marx absorbed Nova's power to revive his dead body and become even more powerful than him, with just standard abilities (Or not... spitting stars works just fine), killed Magolor after