About the Emperor [Major Spoilers for 4.4]

[Iscah]

Yes, that's the thing. He didn't say Solus was replaced by an Ascian or was controlled by one. He WAS an Ascian.

To be exact, he said the founding father of the Empire was an Ascian.

There's still leeway there in that phrasing for either interpretation: that Solus the man directly became a Ascian, or was merely a 'mask' for the Ascian who was the true founder.

But we've also seen that the Ascians have taken corpses that looked "fresh" I guess for lack of a better word.

Bodies seem to 'keep' remarkably well on Hydaelyn.

For a story example (no time bubble!) from the Alchemist questline...

Severian has been trying to revive his beloved W'nahja, who died in the Calamity. Five years have passed, and she looks like she's merely asleep.

Perhaps there's some sort of alchemical preservant involved, but then the Ascians would doubtless be using it too.

Also to note: Ascians were prior Echo users and/or Warriors of Light that for some reason decided to side with Zodiark upon realizing some epiphany.

I think that's still just an assumption at this point? There were hints of it with Unukalhai's nature in the Warring Triad quests, but not outright stated.

Now we know that Zenos and Varis aren't related [...]

"Now we know"? Do you mean specifically in conjunction with your "Solus never existed" theory or do you think the game actually stated that as a fact? If so, where?