Roger doesn’t matter anymore - it’s about Joy Boy now lol
IMO, giants were the original population of the planet.
There were good giants and bad giants (like: no shit!).
Nika represented all that's good with the giants.
Then came the half-giants, or buccaneers. Some were good and some were bad. JoyBoy represented the best of the halfies. He also inherited the will of Nika, AND had fate on his side. But there were others like Joyboy who either didn't inherit Nika's dream or didn't have fate on their side.
Then comes the current era, with humans, or short giants. Luffy represents the best of this era, he inherited Joyboy/Nika's will(s), AND has fate on his side.
But he isn't alone.
Roger, too, represented the best AND inherited the will, but didn't have fate on his side.
BB is NOT the best, did NOT inherit the wills, BUT fate seems to be on his side.
So every few generations, there seems to be a threeway competition between those embodying The Best for the People, Almost the Best, and the Best for the Self, no matter the consequences on the rest.