Nah! Luffy and clark are pretty much alike. Jon and luffy have nothing in common. Jon isn't an agent of change, clark should be. Jon is pretty much positive arc character or should be. He is there because jimmy isn't being used. Luffy is like idiotic selfish version of the goldenage superman or golden superman is like intelligent heroic version of luffy. They are both straight arrows honest, blunt, to the point and reckless. Not to mention dreams and freedom is what they are all about.Luffy and clark suck at diplomacy or don't really give speeches.
I don't know what your problem is with luffy after timeskip. For me, one piece is still pretty fantastic. Jimbei is back, joined the crew and all hell is going to break lose with kaido and bigmom. Comparing that world to Superman's world would be an insult to one piece. They are not on the same level or playing field. And i do believe, current superman wouldn't measure up to luffy as a person. That's just my opinion.
It would be funny, if like you say jon does become like luffy. Well, that would be big head ache for clark. Why? He would be running around causing all kinds of chaos. He would be taking down dictators. Taking countries under his wing.Punching the day lights out of any racist that causes trouble and not willing to reason. Ending things that causes slavery, human trafficking... Etc. He would beating up corrupt officers, politicians... Etc. Jon wouldn't give a damn about rules or protocols or plans.He would be stealing from every rich person and give it to the poor. He would punch delinquents, lazy bums, gang leaders straight and make them do real work and take them under his wing need be. He would be running around reckless without a defence punching through any wall, that's in his way.Even if he breaks his hands in the process . All in all, jon kent would be infamous and controversial. The media will despise him and the police, heck! The military will chase him. He would be praised by those close to him and hated everyone else. Clark would himself need to catch him. Furthermore, if clark does do anything to restrict jon's freedom. Jon would either run away or fight him or do both. It might even lead to clark either being forced to kill jon, by his "superiors" . That is, if he can. Essentially, darkknight returns this time with his son. Either way jon would be something clark can't tame or reason with or control . Clark would become garp. There isn't any possible way that's going to end well for clark.do you really wanna pull on that thread? It won't be pretty.
There is a reason The initial is "d". It can mean the devil. Current clark who is the embodiment of the messiah,would be at odds with jon.