I'd say you're very wrong in thinking the average height is that small. There are very few sub 5'10 players in the league and it's likely the biggest league. The Junior A leagues are small(BC/AJ/SJ/MB)) because the smaller players simply can't handle the physicality of the league or play fast enough to make up for their size. Even for the bantam draft unless the kid is at least 5'7+ at 15 they aren't going to get picked unless they are extremely talented
I was going by an old THW article. I'll go by EP.
In the Dub 11 of 22 teams have an average height of 6'0, 1 team has an average height of 5'11, 8 teams have an average height of 6'1 and two teams have an average height of 6'2. Which means the average height of the WHL is 6'0.50
OHL has 10 teams with avg height of 6'0, one team at 5'11, and 9 teams at 6'1. Which means an average height of 6'0.35
QMJHL has 10 teams at 6'0, 5 teams at 5'11 and 3 teams at 6'1. Which means av average height of 5'11.61
USHL has 15 teams at 6'0 and 1 team at 5'11. Which is an avg height of 5'11.94
So looks like the WHL is actually the tallest now. Propped up by Lethbridge and Seattle having an average height of 6'2. If those level out at all it would be fairly even across the board with the Q and U having
We know for a fact that based on combine height testing that teams often round up when measuring players and in some cases we've seen players listed a full inch or two taller than they actually are. So I would not doubt that all 4 leagues are skewed a little bit higher because of it.
Just for shits at gigs I'll check out the Junior A leagues.
BCHL -6'0.06
AJHL - 5'11.4
SJHL - 5'11.83
MJHL - 5'11.73
Interesting that all teams but the AJHL are taller on average than the QMJHL.