Revelations from Patch 4.4

[Rocl]

Reply to the above:

More MSQ thoughts:Elidibus called Varis "Father" there as a reminder of his place. He's expected to issue the orders he's told, and maybe not be quite so obvious that he loathes the man who's supposed to be his son.

And yes, another Ascian could just possess Solus, but one, we don't know how many Ascian Overlords there are

Taking for granted you meant Varis here, but it's important to point out we don't necessarily need an Overlord to take control of a body. Black-masked underlings raised by Lahabrea were more than capable of running around in mortal flesh during the Heavensward SMN storyline. At worst, the Ascians would have to kill Varis to let an underling possess him--not sure why they wouldn't, honestly. There's guards and all around Varis; we see a conspicous red and blue-garbed pair of soldiers flanking the Imperial Throne--yet these guards, while seemingly shocked at Solus at first, go back to not caring really quickly. Elidibus even talks about possessing Zenos in front of them and they don't care. What the hell? I digress...

and two, someone has to be the face of the Empire, and do all of the mundane business of rulership that the Ascians certainly aren't going to bother with.

To be fair, while he may not exactly be fond of the work, we have to assume Solus has done the mundane business of rulership before and is capable of doing so again. He founded, and to the best of our knowledge, ruled the Garlean Empire for over fifty years.