I'm going by the current justifications on Usopp's profile. His current justifications don't support him scaling to Pica.
As for
Usopp's reaction to Pica, he is way more terrified and would have been crushed flat along with the others if not for Zoro's intervention. I don't like scaling people based on just their reactions without solid statements or feats, but clearly Usopp is way, way out of his league when faced with Pica.
Even without Pica himself,
just the rubble alone falling on top of Usopp forces him to shout for help. We could probably calc this too just to find the energy of the mass of stone falling on them.
So I think we ought to try a little better than just "Hody Jones = Usopp = half of Pica".
If Post-Timeskip Usopp gets hurt by a Town level explosion, and your logic is "Usopp was afraid of Hody Jones, therefore Hody Jones can hurt him." then that doesn't necessarily make Hody Jones higher than Town level, right? It doesn't rule it out, sure, but I don't know what your aversion is to using feats here.