We're pretty obviously using two very different definitions of parity here.
1. The worst teams have win percentages that are relatively close to those of the best teams. Even in the most lopsided matchups, it's not uncommon for the underdog to win a game. If you go to a game, even in an off-year, there's a reasonable chance that you'll get to see your team win.
2. Season-to-season, the standings change dramatically. Even the worst teams can be relevant within a year or two if they make the right moves. If your team sucks, there's still a reasonable chance that when you tune in next year, they'll be great. There's also a good chance that the dominant rival team you hate will be bad.
Baseball has pretty good parity under definition 1. Even if your team is very bad, they'll still beat good teams frequently enough to be entertaining. There's enough random chance in the game that you genuinely need a marathon season for the best teams to emerge.
Baseball's parity is frustrating under definition 2. And it's always going to feel that way as long as major-league teams are supported by multi-tiered minor-league systems and players are developed for years before joining the roster. It takes a long time for a bad team to rebuild. It's especially hard to take when rich teams are able to gobble up free agents and seem to stay competitive forever.
I have no idea which is better or more important. I certainly appreciate that baseball is pretty good under definition 1 though.