I haven't completely read your post yet, but i already found some flaws in your theory.
In this "dark future" of the vex, you question, how the vex would've dealt with the almighty but, in the pefect world of the vex, darkness nor light exist. Because those are factors the vex can't calculate in their simulations.
Only the world as they (vex) see fit, exists here.
Because there has been neither light nor darkness in this situation, the red legion had no reason to come to Sol (our solar system), because there was no traveler to persuit for the red legion in the first place.
I could be wrong ofcourse, my lore is a bit rusty.
English
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<Osiris says we need to stop Panoptes in order to stop the Dark Future. The Dark Future is or will be a reality. Panoptes was trying to find out how to do it. It must've gotten close because everyone acted like this was an immediate threat.>