Havn't kept up with this discussion outside of the initial claim that Rayleigh "wasn't important", but wanted to comment on it anyways: I agree with his 500 reveal not being anything too special. Rayleigh became a major important character after the fact. His end-of-chapter reveal wasn't really that awe-worthy for a 500 chapter mark, and that's not really that bad. Milestone chapters aren't really needed at all.
Fair enough. I am not disagreeing with the milestone chapters not being necessary. I simply disagree in that Rayleigh is at this point any less important than Whitebeard. So yeah Whitebeard was epic and shaped the world that the Strawhats are in. But Rayleigh shaped the Strawhats into what they are now. Storywise he refreshed it and gave just about as much new material as any of the big figures, and also enabled us to see that changed world through the eyes of the characters we love..
It's hard to determine exactly how much a single character changes the story, but to say that Rayleigh is not as important as WB or Ace, I have to disagree.