Sundering stuff established in the Q&A

[Absimiliard]

There was no actual proof high aetheric density makes someone incapable of utilizing Dynamis. That was Venat's assumption, but it wasn't able to be substantiated before the Sundering. The WoL is 8/14ths rejoined and utilizes Dynamis far better than just about anyone. Merging with Ardbert actually seemed to increase their compatibility with it, not decreased it. It seems quite probably the Ancients couldn't utilize it because of how their emotions are handled. Beyond that, the lack of suffering in their society simply left them ill prepared for the kind of emotional turmoil one needs before they can access it.

Regarding Emet-Selch and the Sundering: Venat did not have the ability to control who was sundered and who wasn't. The best she could manage was giving one guy a possible out, but it would only work if he figured out what was up and took measures against it. Emet-Selch himself saved the other two. She had probably unknowingly (via failure to divulge information and her general adherence to her preferred timeline outcome) ensured Elidibus and Lahabrea would be in his vicinity when everything kicked off. By aiming specifically for the outcome she'd heard about from the WoL, it's pretty likely all the pieces fell right into place without her even fully realizing how every little action creates tiny ripples that can then influence other actions and their outcomes. It's like ripples on the surface of a pond.