Or a multiverse.
And do you consider mountain busting overpowered?
You are right about apocalymon, usually anime versions doesnt live up to their potential being hindered by character stupidity.
For example, did you watched Digimon 2? Do you remember that the Digimon Emperor was creating a digimon that was like a fusion? He was creating a Digimon that can evolve into Zeedmilleniumon, but at the end Ken (the emperor) chickened out and didnt went for it.
Yet Ken was at the end of the anime nothing but a fodder against Myotismon.
Digimon 2? No I didn't watch that. I only watched the first season and the movies.
I don't consider mountain busting to be overpowered, but I do consider going from mountain busting to universe busting in the span of one evolution to be sort of(actually very) illogical. Unless these universes are smaller than a planet.
Here is an example of the idiocy of powers in digimon:
Agumon shoots beachball sized fireballs and digivolves into greymon
greymon shoots car-sized fireballs and digivolves into metal greymon
metalgreymon a small hill destroyer and digivolves into wargreymon
wargreymon a large building/small mountain buster digivolves into omegamon
omegamon is a casual mountain buster, becomes omegamon x with x antibody
omegamon x can wipe out a universe.