About the Emperor [Major Spoilers for 4.4]

[Lauront]

Except the part where guy who founded the Garlean Empire and sent them on a crusade against the primals was himself one of the immortal wraiths giving humanity the knowledge of how to summon primals and the motivation to put that knowledge to use, founding said Empire specifically so trick people into going to war at the cost of catastrophic global chaos. I think that part may have skipped through the cracks, lol.

But the Ascians could have accomplished that with or without the Empire, by getting Midgardsormr out of the way - Agrius slaughtering him was always a wild bet, and they could've done it themselves, through the use of Allagan tech. Once the seal was broken, they would have but to spur the beast tribes into attacking the city states, and you'd get much the same end result. Nevermind assisting Thordan in breaching Azys Lla, where 3 dormant, very powerful eikons remained. The above would suggest the Ascians were intent on using summoning as a weapon, one way or another. I believe had it not been the Garlean Empire (assuming "Solus" is being truthful), they would have repeated much the same trick with Ishgard, instead. So Theodric is quite correct on the threat primals pose, exactly because they're the Ascians' preferred weapon/catalyst as things stand. The Ascians would have forced primals into being the threat they are, one way or another.

How recently? Nothing suggests he wasn't there for a long time. Solus died in 2.2 I think. And Lahabrea's idiocy was in 3.0 As far as we know Solus was there behind the curtains from 3.1 Onwards.

We don't, really. He just said that at this point, he had been called back into service by Elidibus. Quite when he resumed his earlier duties is, for the time being, unclear. I'd consider 3.1 to be recent, either way.

You're 100% sure that Solus zos Galvus the man and "Solus zos Galvus" the Ascian are separate entities? Solus zos Galvus was born a man, died a man, and was replaced by an Ascian of unknown identity who is continuing to go by his old, dead puppet's name, and is continuing to self-present with his old, dead puppet's body, for reasons unknown? Are we able to conclusively rule out all other possibilities at this time?

Everyone seems to understand exactly that the implication is but none of the lessons given when educating others about it seem to line up.

It's just proliferating and exacerbating that initial confusion, imo.

I'm going to take a moment to go back and re-read and see just how many walls we can feel out.

Which is the point I've been making repeatedly about the Ascians. We don't know enough about them to draw any conclusions as to how definitive their mastery over their host is. The examples we're familiar with are, in some respects, defective or inadequate to draw broader conclusions as to the nature of the Overlords and how they possess bodies. What I would say, however, is that I would not take "Solus's" speech to lead to the conclusion that he was an Ascian all along - from birth - because he gives no such implication. It might be the case, sure, but to me his words appear to suggest nothing more than he took the Republic to an Empire. This most likely occurred after Solus had gained some prominence and when the Ascian took over, if he really did.

So yeah, like you say, we need more information.

When Nabriales is ejected from his host body following the fight in the Chrysalis, his fleshless form appears above it, looking identical to the host body, sideburns and all. What happens with Solus is in line with that.

My hypothesis for now, if only because it seems to explain all these instances most neatly, is that we usually perceive Ascians' fleshless forms as looking identical to the last host they possessed. We know that Ascians' appearances are affected by expectations in some way thanks to Elidibus' spiel in patch 2.1 explaining why Tataru was unable to see him: "Knowledge dictates expectation, and expectation colors perception." (English localisation lead John Crow [A.K.A. Corvinoobus] explains in an interview here that this line was also written in this way to hand-wave away the differences between current Ascian depictions and the shadowless Ascians in 1.0.)

That could make sense - equally, Solus re-formed himself in front of Varis and his guards and then strode off. So, absent total ejection from the host's body (e.g. as effected in the cases of Nabriales and Lahabrea-as-Thancred), and domination over its soul, it remains open, as far as I am concerned, that the Ascian can simply re-constitute the same form. That, or they can summon very convincing illusions. Both make sense given their array of powers.