Understanding the context of both timeline and pararell world is like trying to get into hell via vip pass.
Holy sht it complicated.
But here is what I found.
Pararell's world is basically a different world with multiple timelines.
Inside those parallel worlds there is the existence of prime timeline.
Prime example of prime timeline would be fate stay night branching other fate materials.
The timeline inside the parallel world must be related to each other must be somewhat related to each other.
If zelretch interfere it directly, it would cause the timeline he gaze became true.
Removing all other possible timeline from it branch.( Or some) This is fatal in certain extend because I heard the world use timeline as texture which is part of defensive mechanism
We have know that Avalon exist outside of time, yet I never heard a single mention of Shirou being there in fgo. Not even from Bedivere himself that manage to get into Avalon.
If this the case that goetia wouldn't affected the other pararell world dispite destroying the time tree it self.
And here the kicker, how the hell mash be able to tank the attack from goetia? Sure she is kinda dead, but she does be able to make Fujimaru safe from the blast that cannocally the pure heat from the energy that being converted from infinite possibility of human history?
And fun facts what ever the things that goetia did is only classified as close to the true magic. This kinda logical considering Solomon is king of the magecraft and not true magic.
But yeah that's my analysis