The point I'm making is that Goku is very used to fighting people who are very similar to himself. Kirby just copying Goku's powers isn't enough to give him enough of an advantage to win, and since Goku's also a martial arts prodigy he's got more than enough skill to make up for Kirby having a similar powerset.
That's not exactly how that would work. When Kirby "eats" something it goes into a sort of pocket dimension inside of him. Thing is, this is comparable to the Hyperbolic Time Chamber existing in a pocket dimension in DBZ, and characters weaker than Goku is now were able to escape from there using just the power of their voices. Needless to say, Kirby could probably copy Goku's powers from eating him, but Goku would simply just escape after. That is of course giving Kirby the benefit of the doubt of being able to suck up air with enough force to overpower Goku and consume him to gain his power to begin with.
