It was easily Sanji for the longest time. Nosebleeding mess for FMI. Leg broken by vergo. Trapped by his simp nature at Dressrosa followed by being punked by Doflamingo. Didn't have any real impressive victories at WCI. Got trapped by his simp nature again at Wano. Destroyed his raid suit because of the monster he could become. Which is an interesting juxtaposition against Chopper since he gave up his more humanoid form to be a monster for Luffy.
But he gets a pass as the worst because his super human genes activated so he should be able to fight some stronger (male) opponents from now on.
At the end of Wano, Usopp is by far the worst. Usopp while inconsistent did make some strides during the timeskip. However, Usopp needs to put in some work after his disgraceful performance during the raid. Hiding behind Nami and then telling Nami it is ok to lie about Luffy becoming the pirate king makes him the worst straw hat by far. That cowardice completely shits on his speech in Alabasta against Miss Merry Christmas. Hell if Carrot joins then Usopp is still the worst straw hat. Brook's speech to big mom was fire. Chopper stood up to Big Mom on the Sunny and Queen in Wano. Not to mention using Caesar's alteration to the rumble ball, someone he hates. Nami in the end stood up to Ulti. Man, where is the Usopp that taunted Lucci?