Holy yap sesh incoming: I think one piece is simultaneously overglazed and slandered too much when it comes to the political themes. Obviously it isn’t the genius marxist critique some describe it as (largely due to Oda writing it very incoherently) nor is it the disney “we just need a good guy in power” either.
To me there are a few major themes that stand out; 1) freedom does not come to those who wait, it is something you must seek out 2) Oppressive regimes will do anything and everything to maintain their position, the oppressed can only win through violence 3) you cannot achieve change as a cog in the oppressive system.
We see Luffy inspire countless people to train and become stronger so they can be free to pursue their dreams, whether it’s Koby joining the marines or the straw hat crew (mainly nami, sanji, robin, namely
Every oppressive force Luffy has encountered has been defeated through force, and it has become painfully obvious that Garp has done nothing to change the system from the inside. He knowingly works for the literal devil
There is an obvious through line here though, oppressive systems only respond to violence from outside of the system by people who are willing to take their freedom back. This is not a disney theme, this is inherently revolutionary. One piece touches on a town of union workers with an elected mayor, a town ravaged by a lack of healthcare (drum island), the generational trauma caused by slavery, colonialism in skypeia not to mention the comically evil world government
However I do not believe Oda is intelligent enough to discuss these topics in depth, he does everything he can to make Garp look good, he is lowkey pro eugenics with only the strongest blood lines ever producing characters of consequence, alabasta and other “evil monarchies” were returned to the original & “good monarchies” to great applause.
In summary, Oda’s themes are revolutionary but childish. One must fight from outside the system to gain freedom but do not ask him to envision what follows the defeat of the oppressor as it will be some version of the status quo.