This wasn't really a function of NFC dominance, in my mind. The real issue was two-fold:
1. In the 1980s, the AFC went through several years where the AFC team that would match up best against the dominant NFC teams would lose in the playoffs. The Broncos of Super Bowls 21 and 22, for example, were not great teams from top to bottom but had some solid players who came up big in the playoffs. I still say to this day that we may have seen two of the best Super Bowls of all time if the Cleveland Browns had won those two AFC championship games. Those Browns were built like some of the best NFC teams of that era.
2. In the 1990s, the "run and shoot" took hold in the AFC -- with disastrous results outside the conference. Maybe they were just 10-15 years ahead of their time, but that type of offensive game plan didn't work well in a tough game against an opponent with a great ground game. The Bills demonstrated that in spades, in both victory and defeat. The AFC wild card game against the Oilers in 1993 exposed all of the flaws of this offense; Warren Moon threw for over 200 yards and 4 TDs in the first half alone, but Houston blew a 32-point lead in the second half even while playing against an injury-depleted Buffalo team. The "run & shoot" offense of Houston was exposed badly, as it was completely ill-suited to mount time-consuming drives with a running game. That may have been the first NFL team in my lifetime to go through a season without a tight end on the roster. They just lined up with four wide receivers and threw the ball downfield all day long.
It wasn’t a function of NFC dominance it was a function of dynasties. Half those SBs won by two teams. The NFC as a whole wasn’t that dominant, cross conference was close to 500. But there were the mighty dynasties that were just plain better than everybody else. Outside of those dynasties the NFC wasn’t that great (especially not the NFC Central, home to the twice annual Bay of Pigs games where the incredibly awful Packers and Bucs played terrible football twice a year). That’s what everybody forgets about that era, they remember the dynastic teams playing great football in their playoff matches, they forget that the rest of the league mostly was terrible and played unwatchable football.
Dynasties are boring. Just look at the NBA. 2 years ago I said the only way we weren’t seeing a rematch in the finals was if Lebron or Curry got hurt, with an outside chance of the Spurs figuring out the Warriors. Last year I said the same thing. I’ll go even further and say that the only way it’s not Warriors Cavs NEXT year is if Lebron or Curry get hurt with an outside chance the Celtics figuring out the Cavs (forget the Spurs, they’re done). The entire NBA season and most of the playoffs have no meaning to the league. And they’re unwatchable because there just isn’t the talent on those other rosters.