There is definitely parity in the OHL
Just look at OHL title teams and how many times each team has made it to the finals since 2000
London - 4 OHL Titles, 5 Conf titles
Erie - 2 OHL Titles, 3 Conf titles
Guelph - 2 OHL Titles, 2 Conf titles
Kitchener - 2 OHL Titles, 2 Conf titles
Windsor - 2 OHL Titles, 2 Conf titles
Barrie - 1 OHL Title, 4 Conf titles
Flint/Ply - 1 OHL Title, 3 Conf titles
Ottawa - 1 OHL Title, 3 Conf titles
Ham/Belv - 1 OHL Title, 1 Conf title
Oshawa - 1 OHL Title, 1 Conf title
OS - 1 OHL Title, 1 Conf title
Petes - 1 OHL Title, 1 Conf title
Nia/Miss - 0 OHL Titles, 3 Conf titles
Missy - 0 OHL Titles, 2 Conf titles
NB/Bram - 0 OHL Titles, 2 Conf titles
SSM - 0 OHL Titles, 1 Conf title
Sudbury - 0 OHL Titles, 1 Conf title
So over the last 20 years, 12 different teams have won. The only true dynasty is London.
Kingston, Sarnia, Saginaw have never won a conference or OHL title.
Reality is that across the league in any given year there is parity.
Heck just look at the conference finals this year. Guelph was a 7th seed, 30 win team last year. Saginaw a 8th seed, 29 win team. Ottawa was an 8th seed , 30 win team and Oshawa was a 5th seed, 36 win team.
That’s the only parity that matters. Hockey is hockey and every single year the playoffs will reflect that. A series that lasts 4/5 games might not be indicative of a lack of parity but rather one team might have just won the close games. And since we are dealing with kids in junior hockey and a lot of sell offs/trades each year, we can’t expect round 1 to ever be more than an experience and money builder for 7-8 seeds. Maybe a 6th seed can be competitive and sometimes win. But the conference finals and OHL finals show new teams virtually every single year.
And we typically see good series in the conference finals and finals. 2016 the exception. But generally there are 6/7 game series in at least one of the conference final rounds and the finals - regardless of outcome, are good games and competitive. Missy lost in 5 in 2017 to Erie but were an OT winner away from forcing a game 6. Same said for Erie in 2015 loss in 5 to Oshawa, just an OT goal away from a 6 game series. SSM/Hamilton was very close last year as well
So imo the parity is good across the league on a year to year basis. In terms of playoffs, it’s expected that only 4-6 teams actually have a chance on any given year. Sometimes upwards of 8 teams could win but also sometimes only 2-3 teams have a chance. But that’s the nature of the cyclical year that Otto mentioned and the year to year parity with teams. Trades make it that way. But all things considered, round 3/4 usually are close and competitive (regardless of games played in those rounds). And sometimes round 2 offers up a really good series or 2.