What did I just watch?

That should have been episode 1000.

If/when One Piece is 'redone' as a Kai version here in a few years, if it could be animated like that... anime wouldn't be niche.

Maybe the Toei hackers chipped in and stole the storyboards, contracted out to independent animators, and re-injected this back in? The last episode with production rivaling this was the finale of the Katakuri fight back in... early 2019? Though Wano as a whole has had better production, this was something else, start to finish!