Zoro will cut him in half.
I'd say Luffy did go all out on him. He wasn't fighting for his life but it was probably one of the most serious fights he's ever actually had. Take a look at how he dealt with Bellamy compared to Usopp, the bullet attack he finished Usopp off with would have been more than enough to one shot someone like Kuro.
You forgetting that Luffy wasn't going all out on him
I feel like Usopp could probably take out everyone aside from the monster trio.
Nami would be fairly easy, he designed her weapon and she's physically weak.
Robin's extra limbs take damage as if they were attached to her. She got pushed back by the army in Alabasta. I imagine her range is limited and Usopp could snipe her from a distance as long as she didn't sneak attack him before the fight starts.
Chopper could be easily tricked, or his heightened sense of smell taken advantage of. The rotten eggs held Luffy back, they'd probably harm Chopper. Monster point is still uncontrollable and I assume moves slow. Usopp should be able to wait it out.
Franky needs cola to fight effectively. Some of Usopp's plants such as the humandrake, devil and impact wolf could lock Franky down, force him to use his cola reserves to fight them off, or destroy his cola outright.
Brooke I'm not really sure, I still don't have a proper feel for how strong he actually is but I could see Usopp winning easily.
We've not really seen enough of Usopp to get a feel of how strong he's actually become. I don't think he'd be able to take out any of the monster trio but i'd put him around Water 7 level Sanji.