I'm not saying he invented nickel as a defense, simply he was the first to employ it as a base defense. Team's obviously have film of nickel packages used as situational defenses but not of an actual base where on first down its a 4-2, second down is a 4-2, and third down is a 4-2. It was a different look that teams didn't have film on that allowed a lot of unique looks and countered the popular offensive trend of three wide receivers being the new base.
Payton then stuck his nose in to meddle, however none of it changed the fact the Saints in 2012 through 2016 had an aging defense lacking talent with poor position coaches. When the defensive coaching staff overhaul happened in 2017, the whole defense turned around. Talented players were being developed by good position coaches leading to a very impressive run and what should have been a second Super Bowl appearance and possible Lombardi #2.