After thinking about it... I think the issue here is that oda doesn't have any fucks to give. He will rush the story so hard you'd think it's running on pounds of cocaine and meth per second. Consider the wano arc.
- First we see G4 luffy get speedblitz and one shot by first form kaido. Then a training montage later we see base luffy surviving kaido. Then several pounds of cocaine later we see CoC cladding luffy holding his ground against hybrid kaido. And of course G5 luffy eventually overcame kaido.
- Zoro went from wherever the fuck he was to being able to sustain nigh yonko level combat for a time due to emma shenanigans.
- Sanji has zero feats and shit development to speak of during the new world. Shit enemies during fishman island, no feats during punk hazard iirc, no enemies during dressrosa other than a tiny confrontation with doflamingo, spent 900 volumes baking a fucking cake during FI, and then didn't do shit in wano until he fought queen. Whom he defeated due to convenient mutations.
- Franky has no meaningful feats during the NW just in general. His only fight before sasaki was sr pink. I don't think much of the topo robi in general but even that was unearned for franky.
- Robin defeated black maria...
So this isn't an issue of time. Oda could as easily pull ussop using CoA and CoO out of his ass as easily as he did for sanji, franky and robin. It's too late for any of the characters to have any meaningful, systematic progression and the fact is that the story will soon need ussop to hold a candle to actual yonko executives. So he will.
I will also add to this:
- Law randomly getting strong enough to engage with Yonkos and tank thunder bagua from hybrid Kaido.
While the last we saw of him (in Dresrossa), he was getting dominated by Doflamingo