Uh, no. They were very much a separate people. Our player characters are the cut up fragments of the original Ancients that evolved into entirely separate species from the original ancients, so yeah, they were killed and replaced.
When we face Meteion we're at 9/14ths. If she divided the world to make us able to interact with dynamis, why not inform everyone of the threat and propose that solution? Not only would you have a world full of super wizards attempting to solve the actual problem. Given they only need a 1/2 reduction of themselves to control dynamis, they could have consensually reduced themselves to two parts which would have maintained far more of what they were than what she did. And it would have been done with a world of geniuses working together rather than a psycho and her 12 simps murdering everyone.
And if you want to argue that they wouldn't have done that...75% of their population gave up their lives to save their world. If there had been a way for them to make a sacrifice where no one had to die, if only they'd known about the problem, nothing about them suggests they wouldn't push through, because they were actually incredibly strong regardless of what Genocydalyn said about them.
Stop blaming the Zodiark summoning because she let that happen as she needed it both as an excuse to get her simps to sac themselves for her and to protect the planet for 12k years after she murdered everyone.
Imagine what would have happened if they listened to her and didn't summon Zodiark given she never informed them what the actual problem was or given them forewarning so they could prepare a defense ahead of time. They would have become entirely extinct. Obviously, that wasn't her goal, so she didn't really want them not to summon Zodiark. She just opposed it to create the strife needed to weaken her people so she could murder them all.
If at any point the Ancients pimp shrugged and did what Venat wanted them to do, all life in the universe would end, so clearly that wasn't her real goal. She set them up to be slaughtered.
ETA: I don't believe being able to control dynamis would be enough. I think that given the solution, people who overcame each type of despair Meteion had experienced would be needed. Like purposefully exposing someone to a disease so that they create antibodies. But had Venat informed people of the problem, and the likely solution, a portion of them could have volunteered to be sundered and run through her torture simulator to learn the lessons needed to save the universe. But instead of telling people and working with them, she took it upon herself to kill them, bury their culture and history and make herself a supreme deity. As my character said to Emet-Selch in my headcanon, "any plan that requires murdering babies in their crib is a bad plan."