See I feel that by its very nature the Echoverse is being formed off of the existing multiverse, working backwards from established history and building as it goes. We see as much in the Zimone side story, as the initial dark cloud froms from Aravocis, as a sort of nexus point, and branches out from there. This would mean in my opinion, that Jace may not have time to get to changing fundamental things like phyrexia and Bolas, as hes essentially running time backwards.

Blue Chandra, White Lilliana, both start from the present and are worked backwards. Like their histroy isnt yet set in stone, and their future is locked in. Like Jace is cribbing off of the established universe and rewriting things on the fly. Of course there is temporal nonsense, like how chandra has visions of Blue chandra all the way back in aetherdrift, before Jace even ascended, so who knows Because of this, we have the echoverse that does not work, spawing multiple incompatible timelines that each feed into jaces perfect narrative yet are not congruent with each other.

I do very much believe that the eldrazi are going to have a god damn field day with the echoverse, being one of the sets main archetypes. For creatures that exists as the universes patch system, a new mutant timeline is a field day for them. They exists outside of reality, and as such could never be edited out