Probably an unpopular opinion but here it is: 6's Matchmaking was a massive fucking bone for Valve to throw us. We need to keep trying to play it and give feedback so they can continue to update it. One of the most important feedback issues is weapon balancing. I think one major thing stopping Valve from backing current 6's stuff is the long list of banned weapons. The new global whitelist is a good start, allowing a few of the more toned down unlocks. But we need to just drop that shit entirely. It'll probably be a really frustrating couple of months or whatever, but I'd consider this "growing pains." I think they're using game data to adjust weapons, and not looking at whitelists posted in competitive website forums, and reading through league admins justifications on why certain things are banned. My primary reasoning behind this assumption is the Sydney Sleeper. We've had that shit banned for YEARS and it gets buffed? I think it was so underused that they assumed it was bad, or maybe banning it mid season 5 years ago was a kneejerk reaction and the gun actually isn't THAT incredible, it's just frustrating to play against when a team plays around it well.
Another major issue is class limits. I don't honestly know if the current league limits are a good idea anymore. I personally think current 6's is fun to watch. If we remove class limits and unban all weapons, it probably won't be very fun to watch... At least in the short term. Again, I would hope that there would be a reaction from Valve to add a class limit 2(didn't Blizzard do this for OW?) We may in fact just have to put up with playing "their" format of 6's, until they realize how flawed it is, and adjust it into something more enjoyable.
Maybe I'm completely wrong, who knows what their actual decision making process is. My current thoughts however are that if people want competitive to grow and want developer support, then our community leagues and websites that support competitive shouldn't remain so different from the competitive mode they've given us.
Current timeline of potential ESEA Open player:
Try competitive matchmaking.
Make friends, Make a team.
Look for league to join.
Only leagues are VASTLY different from matchmaking.
Team disbands because 3/6 players are Heavy, Spy, and Engi mains. Unwelcome and innefective in current ESEA format.
Tired ramblings but probably fairly accurate.
TL;DR: If Valve hasn't embraced ESEA 6's and sponsored LANS like iSeries after like 5 years, they won't. Unless the format changes.