@soundtea
Very confusing…
What little is clear was that the problem was not
caused by universes “being more alike”, it was because of ponies (and objects, before Starswirl stopped transporting
things as well) from one universe existing in the wrong universe, upsetting balance. The
effect was objects from both dimensions becoming linked and experiencing similar forces when they should not. This eventually culminates in a large scale collision as both entire universes start merging together.
The freeze-in-crystal solution was initially to simply contain Evilestia and had nothing to do with fixing the underlying cause, until Celestia showed up and suddenly it became about “restoring balance”, which makes very little sense admittedly. Once a rift is made connecting the Celestias, putting them back in the correct world isn’t enough for balance, because… the rift is the problem? How does freezing them fix this? And Luna also was also affected so would it have even worked without freezing her also?
As for the Elements of Harmony solution, while at least targeting both Princesses, doesn’t have any logical basic for fixing the merging universes. Even Sombra’s vague explanation of why it would work seemed based on preventing just the injuries that the rift causes, not fixing the underlying problem, and certainly not fixing the entire universe.
The only way I can interpret freezing or the EoH both being solutions that “restore balance” is that it works by making the offending objects (in this case Celestia and Evilestia) become so alike that it somehow reconciles the paradox and unlinks them. Still not an entirely logical theory. No matter how you look at it, the solutions presented are strange and unexplained.