Luffy being "the chosen one" has been telegraphed for over 500 chapters at this point.
The foreshadowing and set up between Luffy and the chosen one/Sun God is undeniable.
Where it falls apart for me is making the Gum Gum fruit the Nika Nika fruit, and Gum Gum doesn't actually exist.
And the World Government is the one who made that choice.
And they've been after it for 800 years.
And despite their vast reach and intelligence agencies they just recently figured out the guy with a strawhat who is a D, who is related to Garp/Dragon and has stretchy powers might have the Nika fruit?
Or they've always had a good idea Luffy had the fruit and decided to chill and see what happens? Despite showing how ruthlessly murderous they can be with mere hints?
The only explanation that's somewhat satisfying is they're lazy and incompetent. Or Garp/Shanks pulled some serious strings to protect Luffy early on. Everything else is too sloppy.