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Here we see Ichigo being curbstomped offscreen by a random sternritter. Which begs the question, Why is everyone trying to get him to fight Yhwach? Yes, he's the Main Character, but Urahara and the others don't know that. As far as they know, he's just the strong guy who is completely incapable of fighting Yhwach.
At least the plan made vague sense against Aizen, since Ichigo wasn't affected by Kyouka Suigetsu Ex Machina. But Yhwach can directly control Ichigo through Quincy Blood Ex Machina. If you don't believe me, ask the Soul King, who isn't half the man he used to be since Yhwach first demonstrated this power.
A more viable strategy, would be to leave Ichigo to die while Askin explains all the inner workings of the Wandenreich, and having the occasional Coffee Break, then to have Urahara and everyone else go Bankai and jump Yhwach at once. Obviously, this wouldn't work either, but at least you aren't sending the kid who already killed God because Yhwach wanted him too.