I do agree on a lot of things you said. The fights are just the same, characters have barely changed in the psychological department. However I like the things they treat in OP.everyone in those mangas always powers up to protect their shit. they do that in fairy tail as well, even though half the power ups are temporary in fairy tail or only show leftover effects 20 chapters later.
luffy does not fight more maturely though, he just doesnt. its the same as always, one attack after the other, now randomly enhanced with haki that apparently is a swiss army knife among abilities, similar to the sharingan in naruto (it makes your body stronger, enhances your muscles, has 200 jutsus you dont really need to train for etc etc).
or do you think it was reasonable to assume that sucking in all of ceasars poison gas would work out fine and dandy because he was already poisoned once in the past and he somehow is able to channel things from his lungs to his ears now?
or how there was a plan and he completely ignored it to fight in that tournament?
or how he still ignores pretty much anything just as he always did? like not making big mom angry and then even angrier.
hes just the same airhead as he was when the show started. granted, thats exactly what people want in those long shonen series. they just want it to go on the way it did.
The whole Pirate vs the World government is interesting at best. I like how they also introduced a few ruthless characters that are "upholders of Justice" and they will do pretty much anything to kill the most notorious pirates. (Akainu)
However, they aren't actually better than the pirates they are trying so much to kill, so there's irony in that. XD
The introduction of the fishmen also brought something I would never think they would show in anime.
Racism, pure outright discrimination that isn't founded on any purpose. Reflects a lot in our world too.
It also introduce a whole lot of concepts that makes OP rather interesting, however there are lots of weaknesses as well.
All the characters have interesting goals and a lovable background, (Nami and Robin, being my most favorite due to it's seriousness)