What is wrong with BB rising to such levels of power so quickly ?
The man was not a rookie. He sailed with WB for years so he was always in the NW. He has 2 of the most powerful DFs in the series under his command, and more importantly he had a plan, one that was years in the making.
Shit, Shanks himself took an injury from BB, and that was before he had the gura gura no mi, so the guy is no joke.
Given the knowledge and experience he gained while with the WB pirates it's not surprising that he was able to make the right moves and be recognized as one of the four so quickly.
Knowing Oda though this would probably make too much sense and throw us for a loop
BB stated at the end of MF that the time would come for him to take on Shanks. Shanks is not only one of Luffy's friends and benchmarks, but he has beef with BB, evident by the talk he had with WB when Ace left to take revenge on BB in WB's name. He will most likely be killed by BB, raising the stakes in the inevitable Luffy vs BB fight.
Anyway, my ranking is:
I won't even rank BB yet, but one thing that can't be forgotten is that these 4 keep each other at bay. The difference in power will not be enormous, though a hierarchy most likely exists. Kaidou met with Shanks on his way to intercept WB before the war took place and lived. That supports the small power gap from my point of view.