The change in the flow of time between shards, by all appearances, appears to be 'always forward but at different speeds'. So no, there would never have been a point where 'time dilation' means there's two Igeyorhms.
And the Ascians are essentially tied with the Garlean Empire for being the longest-lived, most written antagonists in the game. Hell, I'm pretty sure their per-word story weight outdoes the Scions. You might want 'finer details', but let's not act like they were cut short and not given enough screentime to discuss everything important: they had more than enough space for the writers to cover as much ground as they wanted. Anything they didn't cover was stuff the writers didn't see as worth it, not stuff that they just 'didn't get to'. Especially something like this, which I'm gonna be honest, is in-the-margins ruling nonsense for a situation that never happened.
Also, this does make me realize that, yeah, it's a simple matter of who we're talking about: the Ascians are self-important and exalt a very specific governmental structure that they all used to be part of (at least, to a relative degree). They would not elevate more than thirteen core Ascians because they just believe that thirteen is the correct number. And in fairness, thirteen of them did the job pretty well for about twelve thousand years! We frequently forget that on their time scale, the Ascians went from 100% to 'utterly turbo-dead' REALLY fast, it's only during the events of the game that they start dying.
And as for the black-maskers, I feel like they're pretty much done. They were a cult controlled by their leaders, and with those leaders gone, I always just assumed they burned out. Might be nice to hear it in text, but I know I'm not begging for them to become big antagonists, especially because they'd feel so disappointing. The Ascians are done, they had their big dramatic climax and finale; do we really benefit from introducing more, lower-budget Ascians? Because to me that feels like shark-jumping.