If current Usopp replaced his pre-timeskip version in the story, nothing would change.

He can’t hurt crocodile. His plants won’t break through daz bones steel body. None of his suit would do anything against nightmare luffy or moria.

Enel can’t be damaged by him.
He can’t save anyone at sabaody and the pacifista smokes him when his bamboo snaps to their hardened body. His bomb trick won’t work on all of them if they just simply punch him instead of opening their mouth.

Luffy still beats him because current usopp doesn’t use impact dial anymore (bro used moves at beginning of timeskip only to never again)
Current usopp isn’t as strategic and doesn’t prepare and plan since oda IQ drop from going senile.

Foxy negs him still.
We have seen no improvements to his speed at all. He got caught by civilians when shooting sugar. And was physically too weak to push them off.
I think he wouldn’t even shoot the flag anymore since he doesn’t snipe anymore.

No seriously. He would have no impact on the plot if his timeskip was in pre-timeskip. People will defend him by writing him out of character and pretend that usopp will use impact dials despite his ass not touching those in over 14 years. He has to act out of character to beat these people. Fight like a genius even though he is a dumbass in post timeskip.