I haven’t watched Into the Spider-Verse yet, but Gurren Lagann is fucking brilliant, IMO. The way that series crescendos into its finale is positively otherworldly. It’s the greatest giant robot anime of them all.
Having met a few animators, I’ve come to believe sections like that are basically sequences that explore animation for animation’s sake, almost in an abstract way. Or like a looong guitar rift in a rock song. It’s a display of the craft during which the animators can try whatever and have fun.
So that’s the way I look at those. Given the overall fantastic animation in the movie, I think this reading is likely not that far off (and Studio Trigger’s crazy stuff is the same, I think).
I don’t think it necessarily works dramatically (I found it too long and dragging the overall tempo of the movie) but I did enjoy it.