I'm not sure how you can say dynamis "solved problems" when it was quite literally the cause of the final days. If anything it was an antagonistic force that our aether-based characters had to find ways to counteract.

Also, in the context of Endwalker, it was introduced very early on through the Elpis flowers and in Thavnair, and explored more throughout the Elpis questline before being central to the ending. And even prior to Endwalker, there was a looming question of what unknown force caused the Final Days; and then Endwalker goes on to introduce and explain a previously-unknown force that caused the Final Days; seems like decent enough set up and payoff to me.