Your "confusion" point doesn't matter, my interpretation doesn't add timeline confusion.
Your interpretation contradicts:
1) The central role of Legerdomain in the multiverse, several lifeforms would also exist without life itself existing in those other universes considering Legerdomain got created together with Ben's universe by the Contumelia under your interpretation.
2) Ben saying he went to alternate universes like Rex's before.
3) Dagon being sealed and unable to enter Ben's universe.
I mean the seal specifically effects Dagon but you'd think if someone makes a portal through which he can send souls then he can also go through it himself despite the seal, so him not going through it must mean that Legerdomain isn't inside of Ben's universe.
I meant the
It was implied to be sort of this place that wasn't part of Ben's universe nor Rex's universe, but nvm now Ig. Also Holiday would have been referring to Ben's universe and Rex's universe, not the Null Void likely.
Chain reaction time bomb? Oof. You know that might actually make sense and would give Ben Prime a central role in the cosmology which is pretty dope. But how are No Watch Ben and Gwen 10 a thing then if the branching only starts when Ben Prime gets the Omnitrix, retroactive effect? Also why is Clockwork necessary if No Watch Ben already successfully rebooted the timestream?
Dagon's universe is an alternate universe created with a different Annihilargh by the Contumelia (or something else), it has it's own timestream.
You're treating Rex's universe as part of what the Annihilargh created, classic mistake. But yes I get what you mean now. Ben 10 functions more like DC, where every "earth" has infinite timelines.