Spoilers for anyone who hasn't gotten up to chapter 967 in the manga
With regards to the iconic Roger Laughing panel when he gets to Laugh Tale, I think the reason Roger laughed when he got to Laugh Tale is because Joy Boy intended his treasure for someone who would live on and lead the world to a new future by overthrowing the World Government.
This would have been extremely ironic, since Roger was terminally ill and had just spent the final days of his life seeking a treasure that was meant for someone else, who would live long enough to be able to change the world.
I think that positions Luffy in a really interesting spot because he has been shedding his life span throughout the manga, like in Impel Down. It doesn't feel like a very Luffy thing to not take the one piece just because he doesn't have very long to live. I wonder if he would take whatever is on laugh tale and through sheer will power force the world to change before dying.
I don't think that Roger was early for some external reason, he's just at the wrong time for him. For all we know, Joyboy's treasure and the ancient weapons aren't directly related.
Im sorry, but are you dumb or are you incapable of reading?
http://www.funmanga.com/uploads/chapter_files/5404/982/55.jpg
It is very clearly and directly said that Roger was early because of Shirahoshi not being born yet. But also, the sea kings know [and told him] he wasnt Joyboy.
Well, that's certainly one way you could phrase a counter argument.