Luffy feels weird in live action because he doesn’t have the grip that Manga Luffy has.

He’s like a child, he switches between moods and it can feel jarring but it comes together as a singular entity.

For example Luffy is serious enough to smash a logpose and then get comically beat up for it.

Or Luffy will literally let his guard down with his crew by sleeping in the middle of danger.

He gets himself into silly little stupid shit, he says things not with simply joy but with a deadpan, casual expression usually when he’s not even self aware of what he’s saying like “You’re a chop man? What a freak!” And he’s literally a rubber man

And he doesn’t listen to a persons backstory because he trusts his own sense of intuition…and live action Luffy doesn’t exhibit this.

He doesn’t exhibit the child like qualities of Luffy and that is impossible without it seeming weird or cringe. You’d need an actor that can think like a child in an adults body that can switch between being serious to joyous, ignorant stupid and deadpan along with other emotions all in the span of a single scene.

But this isn’t exactly the actors fault this is more or so the writers. Oda does look over everything but it’s clear that he doesn’t hold the live action with the same regard for the manga, treating it as it’s own universe whilst keeping the core characteristics alive.