The idea that he'd try to pool Light again already is not illogical; Ascians recycle and course-correct their plans all the time. But something about it feels weird as a writing choice. We've been thwarting that plan since 3.4, and now we're fighting Eden and cutting everything off at the source. It feels so thematically-inclinded towards resolution of matters on the First regarding its instability/rejoining for a while so we can do something else in the story. Like go to Garlemald. Could main thrust of the plan be just, "Meh, umbral everything again"? (Though that could be a secondary goal of the primary being successful, though.)

I think the primary thing might just be...

[A] Cause societal stress / collapse
[B] Keep the Warrior of Light distracted and bogged down
[C] Ideally have one or more of these high-zeal, low-doubt "Chosen" go full Ysayle and not question their actions as they try to murder the Warrior of Light fOr ThE gOoD oF tHe WoRLd