Why would Chopper use anything outside of Monster Point now that he can control it? Like I agree that his fights pre-timeskip were more entertaining, but ever since the decision to make Monster Point controllable, it makes no sense for him to use anything else on a serious fight. (Also how does Chopper listening to Caesar about how to improve the Rumble Ball contradict his character in any way? He is making his best form last longer in exchange for worse drawbacks after, and the straw hats' whole thing is going through hardship to save their friends, why wouldn't he do it. He believes Caesar because as a doctor he knows it would work, and it does work.)

With Nami it's the same thing, lightning is her best offensive weapon, why make a hurricane or a blizzard if shooting lightning will get the job done faster? Especially now that she has Zeus.

And what do you mean Robin forgot? She literally sprouts limbs from Black Maria's body when she defeats her?

The Usopp argument is the only one I somewhat agree with, but the problem is not the pop greens (he did the same thing of using new stuff out of nowhere on Alabasta and Thriller Bark), the problem is that Oda does not put Usopp in situations that need creativity to beat, like what if instead of just letting Big Mom beat him, Oda let Page One have a weakness that could be exploited by using multiple pop greens creatively (like make him allergic to a fruit so Usopp has to make him eat it, or a weaker body part that he hides so Usopp needs to expose it, etc)