Although I am no longer involved in minor hockey, I was for most of my adult life from coaching, National Coaching Certification Program (Hockey Canada) and association president. I was also involved in the early stages of setting up a competitive high school hockey program that travelled to US based prep schools. I operated mostly in Quebec except for the 8 years I spent in the GTHL.
In my opinion, the reason the GTHL produces more players is quite simply that they identify and cater to the elite at a very young age. That being said, it is done a structure that is not being governed by a provincial association that is trying to cater to both the recreational player and the competitive player. The GTHL is a for profit organization and players are not restricted to where they live - as long as it's within the GTHL territory. They attract players from all over the world. This goes on from minor atom. Of course there are some abuses, or parents that buy there way on teams. But go through the NHL and see how many played for the Toronto Marlies, North York Canadians, Toronto Red Wings etc. High level competition is essential in development. They also group players in single calendar years.
Quebec - well they always have to do thing differently and we can now confirm that over the last 10-15 years, they are failing. 20 years ago, they sort of removed high level competition for Atom. They still persist maintaining a 2 year group per category. These characteristics do not promote elite development.
Don't complain that we are not producing players when the structure is not geared for developing elite talent. Some of the individuals coaching competitive teams have no training in teaching fundamentals, development theory, performance science, physical preparation, etc. Don't complain that it costs a lot of money because all elite athletes in a most sports spend more than hockey players.