I think it depends if we are talking about anime Kirby or game Kirby. Anime Kirby has a pocket universe or a black hole for a stomach, so he would never be full and he has the suck ability to eat anything in the area. Game Kirby is more questionable, but theoretically he can keep eating forever. However, you would have to keep pressing down to "absorb". At that point, it would become a question of how fast Kirby can "absorb" what he sucks in vs Pac Man's ability to constantly eat without swallowing, but without any ability to draw food to himself.

What if Kirby eats Pac-Man and absorbs his abilities?

Pac-Man.

Kirby eats to a point then spits out.
Pac-Man never stops eating. He doesn't even have a digestive system. Just keeps chomping.

Ghosts are irrelevant just like people with Kim Possible avatars.

Wow look at all these people who have never played a Kirby game.

"Kirby swallows one thing and keeps it in his mouth."

See me after class.

Yes, I know that you can swallow multiple things in Kirby. But Pac-Man is such an eater, he keeps what he eats 100% of the time!

Sure, all he eats are little pellets and some fruit, other than the occasional ghost which aren't even corporeal. Kirby eats EVERYTHING.

Kirby expands when he sucks in stuff, which means the things he eats use up volume making the amount of things he can suck in finite. He also has to expell stuff to be able to take in more. Pacman is not full ever and doesn't even expand, his eating ability is infinite. How I know this? By having played most Kirby games. Yes kirby can also swallow things making them seemingly disappear. But that is another action that takes time. Pacman just eats continuously and doesn't even need to swallow, giving him the clear speed edge in an eating contest.

Kirby can eat bigger things tho. He can even eat trees, vehicles... and people. O.o I think he would probably eat Pacman.

Yes this is what we call swallowing. Your statement "he has to expell stuff to suck in more" is false for this reason. He does not "expand" when he eats, only when he is holding something in his mouth. He can swallow an infinite amount of "food" which for him includes monsters and bricks. Pac Man actually does pause when eating ghosts, otherwise he is just eating pellets or fruit. I wouldn't have to stop to swallow either if I was eating a single pea at a time or a couple of cherries.

Just to offer the player some challenge.