Why is it so weak? Why are Kyogre and Rayquaza such a league higher than it?

I mean, it's one of the few legendaries that can't fly while Kyogre (for some reason) and Rayquaza can.
It's smaller than a giraffe while its supposed to be depicted as something that creates landmass,
and it also looks like the least mobile legendary in the franchise (besides Cosmoem)