None. Life is a matter of timing and destiny. Brees and Payton crossed each other's paths at the right time. Payton wouldn't be successful without a qb like Brees. Brees wouldn't be as successful without an offensive coach like Payton. I hate this phrase, but it's the perfect storm for both of them.
More evidence to that. We have way more talent and depth on offense than SD had when Brees was there.