It has nothing to do with closing plot threads. The threads you guys are speaking of can be closed in a short period of time.
How many of Wano chapters proactively handed out info? Oda spends chapter after chapter to build up secondary characters. That is why the arcs Post-Ts are so big.
But we won't be needing any secondary character post-Wano. Vegapunk, RHPs and BBPs are all primary players and they won't need ridiculous amount of chapters for readers to feel something for them.
Post-Wano, we won't need the nonsensical plot stagnation for so-called character build up. Post-Wano OP is likely to have a different pacing to pre-Wano OP.
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The Oda can take a bold move and stretch the battles against the WG over many years. Describing the outcome of the main battles, make a kind of chronological description of the war, showing in the manga only the events in which the SHs took part(leaving other events for possible spin-offs), bringing the dream of each of them closer to fulfillment, until finally it is time for the last decisive battle, which he will fully describe in the manga.
But we know that everything will be strictly according to the principle and rules of senen.
That would be possible if there were enough antagonists left. When a war wages on for 100 years, the players change and only the ideology remains.
So, to continue a war for a few years is doable, but it requires a large number of antagonist battalions. Oda could've actually done this to be honest.
He could've gone from Shichibukai, to Yonkou, to Marines, to the WG itself. That would've spread the war over a long period. He could've made it dynamic too: for example, while Straw hats are fighting a Shichibukai, Oda could've shown Revolutionaries fighting somewhere else. Oda could've mixed up the story antagonist line up from one Shichibukai to one Yonkou to a Marine group or any other combination.
That could've worked. But he didn't. And honestly, it wouldn't have felt engaging for many if say...we saw Zoro achieve his goal halfway through the story.