What is Ascian prime? (Spoilers for Shadowbringers)

[Kokomi]

In the optional dialogue with Emet, it's explained that Lahabrea was much weaker because he would constantly switch bodies.

>> Choice 1: Why choose this form here in the first?
Emet-Selch: Well, well, what a curious question.
Emet-Selch: Mortal flesh is but the vessel into which we Ascians pour the elixir of our souls, molding it as fits the occasion. Or not, if we so choose.
Emet-Selch: Be it for a year or a millennium, I prefer to retain the same form until my duty is done. So, after arriving here in the First, I fashioned some hapless body into the man you see before you.
Emet-Selch: Though as your friend over there can attest, there are those of us who forgo such alterations.
Emet-Selch: He was ever the rash one, Lahabrea. Jumping from vessel to vessel. Never heeding the toll it took on him.

[RyuDragnier]

In the optional dialogue with Emet, it's explained that Lahabrea was much weaker because he would constantly switch bodies.

This. He had to combine with a sundered Ascian just to get enough power to take us on because of his switching of bodies. Had he not done that over time, he would have had more than enough power to defeat us himself.

[Daralii]

This. He had to combine with a sundered Ascian just to get enough power to take us on because of his switching of bodies. Had he not done that over time, he would have had more than enough power to defeat us himself.

He was also arguably trying to experiment with Hydaelyn's rules. His exchange with Igeyorhm made it seem like he'd been trying to find a willing Paragon for a while and she was just the first to relent, and after being forced apart he made it sound like it took an immense amount of strength to keep Ascian Prime together while Hydaelyn's laws of reality were trying to sunder it.