So your definition for parity is for every team in the league to get a championship? Of course there are going to be a handful of organizations that get there often because some are run better than others! If you have a quality FO and coaching staff, you can and should have sustainable success. If there is no cap, there is absolutely no need to have a competent office or coaching staff, you just need to have lots of money. Point in case, the Heat.
It is still true that we haven't had a single team dominate the league in the NFL and win repeated championships in succession in recent times, that even the most stacked teams on paper have failed time and time again. The Chickens could win again this year but even then, it won't stretch out to the dominance that you see in other sports and do you know why? Because there's a cap and Seattle won't be able to afford to keep all that talent together. You have your window and take your shot while you have the chance. If you have a great FO and coaching staff you'll get more chances. That's how things should be.