I think you're overrating the OPJHL a little. Most of the regular players in OPJHL go to D-3, only the top go D-1. Only about 70 players from the OPJHL will be going to play d-1 this year with a legitimate shot of making their new teams. Some of these won't make it. There are also 35 teams in the OPJHL. That's about 2 players per team going on to play D-1 hockey if everybody makes it. Also, yes, D-3 has progressed a lot over the last ten years. Also, I think you are referring to club teams, those programs you mentioned are not d-3 as far as I know and also not listed as d-2 or d-3 on the uscollegehockey website.
http://www.uscho.com/d2d3/ . You're right, d-3 is a HUGE step down from d-1 but most d-3 teams would make decent Jr A teams in the OPJHL and good Jr A teams in the EJHL. Hope that clarifies things a bit.