The NHL was by far the best hockey league in the world during that span, not something that "was'nt much". As in, the NHL had all of the world's best players for most of that span and yet the IIHF stupidly organized a tournament, called it the world championship, and banned professionals.
The NHL takes a big part of the blame for the players not going to the 2018 and 2022 Olympics. The NHL takes almost all of the blame for the 2016 World Cup tournament being a joke. Other than that there isn't much to say. The NHL allows players who are available to play in the IIHF world championship. It is unreasonable to expect the NHL to chance its schedule to accommodate a tournament that its customers by and large don't care about, which again is largely due to the stupidity of the IIHF. NHL teams can choose to release players for the WJC if they wish, and honestly the NHL indirectly has made the tournament more competitive for most of the tournament's history. The NHL has nothing to do with the U18 tournament so I have no idea why you mentioned it.
I couldn't care less what happens in other sports. The issues with hockey that you try to conveniently ignore are very old and when it comes to things like the IIHF world championship there is no reasonable solution from either side. The IIHF created a poor situation and to its credit it has taken steps to rectify the problem, but there is no fixing it when it comes to the world championship tournament. I would prefer the NHL owners to stop f***ing around with the Olympic tournament and just release all players for two weeks every four years but I'm not going to cry about NHL imperialism if it doesn't happen and I also won't ignore other big factors like history and the IOC.
A league of 6 teams until 1967 without any visibility in the world. Hockey did not develop in Europe thanks to the NHL but thanks to the international federations. Without them, there would still be an NHL made up entirely of North American players. There was still, during this time, the persistence of an idea that the sport should remain amateur and it could (should?) have been the case. But that in no way explains the current situation.
The reason why players playing in North America are regularly blocked today is not related to this very old precedent. The NHL is the only league to finish in June. Players are regularly discouraged from participating in IIHF tournaments. Even during the WJC, NHL prospects are forced to play low-stakes regular season games rather than representing their country.
The CHL is a satellite of the NHL and is a private league. And the CHL is blocking the development of the U18 tournament. Look at Team Canada. It's 100% the CHL's fault.
Even a guy like Mesar couldn't play for his country because he was forced to go to summer camp. When he has no chance. Just because in the spirit of an NHL franchise, the player has to focus only for his team. As little as possible for his federation and only when the franchise thinks it sees a personal interest in it. So very rarely.
In Soccer, Rugby, Volleyball and Handball, European leagues systematically release their players for international competitions. Systematically.
The NBA and NHL are the only leagues to block players. It requires a grueling fight to gain access for their players.
The expansion of hockey goes through international hockey. Not by the NHL. And international hockey needs the NHL to agree to let other competitions exist rather than trying to crush them.
Things must change. If hockey really wants to diversify, the NHL must invest massive support in the federations. Something it doesn't do.