Sundering and specific character questions. [Spoilers]

[Vyrerus]

I think there is a difference between externally exerting control over a species and actually inhabiting their body.

Not really a compelling argument, all things considered. Though it's obviously true, insofar as yeah, the mechanism for control would be entirely different.

There's what Rosenstrauch said about Voidsent.

There's also the fact that Estinien was able to resist Nidhogg, at all.

Then there's also the fact that dragons are shown to be inferior to Ancients in regards to not possessing creation magic innately, given that Tiamat had to learn it from the Ascians in the form of Primal summoning rituals.

I think I'd chock it up to the Ascians finding a way to control them with neurolinks early on, giving them no need to possess them. Why possess what you can so easily enslave? Especially if it hurts the soul/weakens them.