SERIOUSLY are half of you all that IGNORANT???? Is been stated and written in some ways by Oda that to become the Pirate king means Surpassing everyone and everything, standing at the top… Y'all already know me, I don't pull shit assumptions and "this manga went to shit cuz of this, so I don't want to see this happen in this manga" kind of thing... Here is couple of chapters, some characters who have known Roger and know what strength is says it clearly->
! Mihawk said clearly "Becoming pirate king is tougher than surpassing me"
Not to long ago chapter, Chinjao states the samething- "People like Luffy full the sea(Kid, Law, Blackbeard etc) and they all fighting equally for the same title, but to become pirate king Luffy has to challenge and stand above all this people" I still got more, in beginning of One piece, Luffy says "I will become the pirate king" and Shanks in a serious tune/face replies "That means you have to surpass us, become stronger than us" and Luffy says "yes, I will gather a crew that will surpass you guys"…
Wait I'm not done, let's add the fact that BLACKBEARD will be one of the strongest in One piece soon enough, even the likes of Law, Kidd and co won't stand a chance against him just like Bonney, then Luffy ends up defeating him. I think this enough to show/prove Luffy is now better/surpassed everyone and by not really fighting against and defeating them, after all Mihawk is world best swordsman but he has never fought Vista before....
So after all this and you still think Luffy is not going to be the strongest at the end of the series then quit reading one piece now, and save yourself the time since you don't want Naruto and Bleach to happen allover again. One piece is now Naruto and Bleach.