We are currently in his arc,that's why the build up seems massive. Where's the guarantee that BM won't get as much a build up in the near future. Because there's nothing now? Sorry that logic doesn't speak much to me.
I actually didn't like the build up he got here. It draws him closer to being the next victim of Luffy's crew than I'd like. His buildup so far has been in the shadows, since Bellamy (and maybe even before, I have to check on that, though).
Not that I don't like BM, but it's hard to build her up as DD is. Blackbeard has the jump on Luffy for being a D (a false one, perhaps), having the same reverance for dreams and fate, and has the same view of authority. They understand each other on a deeper level.
DD takes the role of somebody who understands the system and embraces it--not just in words, but in actions. He's got ties in the underworld. He's got supplies going to people like Whitebeard.
He's got ties with the 5 Elders; and, above all, he is also one of the few key characters that understand what's really going on.
That's not something you can make up in an arc. Which is why I don't get how he's brushed aside as a chump with "charisma". I know my special cookies when I see them.