Mmmm... no. We know Kirby's universe is still our universe since Earth exists in it. Since Earth doesn't have any noticeable gravity difference from Popstar we can assume that things like Kirby smashing Popstar and Nightmare being able to blow chunks in the moon are comparable to, well, punching Earth in two and blowing up the moon.
Implying that it isn't just an alternate version of Earth in his universe. Without any other context, you can't assume the Earth we see in Kirby 64 is the exact same as actual Earth.
Because it's definitely not OUR universe...
Also, you can't assume anything about gravity in Kirby's universe, as it's different from game to game. There is literally no given context to it, it's different in accordance with each game and how it's supposed to play.
I'm normally the one thinking exactly that in the back of my mind when people bring him up, but since anything being anything less than top tier usually ends with "a normal person can kick it to death". . .on the other side of the leaf the bosses still aren't anything to sneeze at.
I mean, some of the major bosses are still roughly human sized with that in mind (hello, giant wasp with teleport spam!), and Dark Matter probably wouldn't just stop at corrupting little cute cuddly things.
You have to bend the rules when setting him up against things that would normally be in the same power level since they'd be too big for him to use his main ability on, but to avoid the inevitable pendulum swing where anything that isn't top tier is something you can kick to death, an ordinary human would probably still be messed up pretty bad by him either way.
Now META KNIGHT, that's an eight inch fast flying object with a supersonic blade the size of a butcher knife. He might arguably fare BETTER against the odd larger opponent because good luck actually hitting that before it stabs you in the face. At the very least, that's DEFINITELY something a normal person doesn't want to end up on the wrong end of because eight inches or not he's still not quite small enough for that to be laughable.
Nah, I don't think either of them are particularly impressive in the context of our world.
I mean, at the end of the day, I never interpreted the point of the Kirby series to be "KIRBY IS THE STRONGEST CHARACTER EVAR". Last I checked, it's a game where you play as a pink puffball who mostly has cute little powers but occasionally has convenient access to the odd super move (that's only super in the context of his universe).
Death Battle culture ruins everything, truly.