And about Mock Town, I hadn't thought of that yet as Bellamy being a representative of disbelievers, that does make sense with "mock town" being a town where people mock dreams, but the fact that Oda named a whole town after the disbelievers makes me think it was more of a fluke rather than something that is widespread. It was one town in one arc, next to a long line of town with peculiar characteristics such as towns filled with bounty hunters and the like.
And the whole WB speech, the "One Piece exists" line is just the sinker, if you look at everything he says it's basically that the "D's" are related to the old civilization (like we figured out long before this chapter ) and that one of the Ds will find One Piece and topple the WG with it in a big war. That is why Sengoku is so pissed off. And he also says that this D will not be BB but someone else (=Luffy).