I don't know how you'd measure "coaching parity," but whatever it is, we sure as hell don't have it. Everybody is outright stupid compared to Belichick, and it makes everything about the games real dumb and bad to watch.
Pick a random year in the 1980s and you could have some combination of Tom Landry, Joe Gibbs, Don Shula, Bill Walsh, Chuck Noll and/or Bill Parcells duking it out.
In the 1990s those ranks are thinning, but some are still alive and kicking and even winning titles, plus you've got Jimmy Johnson's dominance, and many guys who were not historically great but still seen as really good like Holmgren, Shanahan, Vermeil. The 90s also had Coughlin and the insanely good job he did with the expansion Jacksonville team, and Cowher winning a ton without a real QB before they got Big Ben, and probably some others I'm forgetting. Some of those guys burned out in 2000+ but at their 1990s peaks they were very respected.
Plus I know I'm leaving some guys out.
Tomlin, Harbaugh, Reid, McCarthy, and Carroll are the best of the rest, but all of them strike me as deeply flawed in various ways, and would all be seen as 2nd or even 3rd tier coaching talents in the 70s, 80s or 90s.