Let's be real, humankind would never meet whatever requirements Emet required of them, making all of his tests just means of coping and justification, keeping him on his massmurdering path to bring back his world and his people. WoL being able to hold in all the light was a completely illogical nonsense test as well that Emet probably knew WoL would fail. And even if it hadn't, ultimately there was no reason for the scions and the WoL to ever assist him in anything. Emet said so himself, if they wouldn't become allies, they would be killed (unless I'm remembering wrong). Either way, Emet revealing that after the rejoinings all the people left would be sacrificed nonetheless just proves that there was no alliance to be had with Emet/the ascians. Even Endwalker-Emet says it pretty clearly: '' the future you seek is not the past we loved '', thus making it very clear that it was never about whether the people would prove themselves worthy, but that they wanted the past and it's people back, not a new race of powerful people. At least, that is my interpretation.
Regardless, I can believe that Emet did feel awful about his actions, but ultimately none of his grievances or woes would matter in the long run. His path was chosen no matter how hard he tried to stray... but then one has to wonder about the final fight versus Emet, if it was Emet knowingly being sloppy, careless and needlessly antagonistic because he didn't want continue anymore and needed WoL to bring him down for good. Either way, he had nothing to lose at that point. Either kill WoL for good and continue bringing back your world, or get defeated and finally get put to rest, potentially knowing that the future isn't it god awful hands in the end.
Was it a battle of WoL and Emet, or the battle of the Emets? The Emet who is tired and just wants to quit, and the Emet who wants his people and world back no matter the cost.