I'm mostly feeling the same about this situation, but I also understand the developers. The initial testing phase wasn’t supposed to get this big. However, some community members couldn’t keep it to themselves, and people began abusing the first invite system. So Valve decided to loosen the terms and expand invitations to let more people test the game.
I think they realized their mistake. People weren’t giving feedback on a pre-alpha game. Instead, they were complaining about the game’s state and playing solely for competition. My point is, most people weren’t there to help test and support the developers; they were there because the game was fun. At the time, there was also a competitive mode, and players just wanted to grind and get better before release.
That’s likely why Valve created the Experimental Branch. From what I understand, it's a more strictly managed version where you’re expected to give consistent feedback and actively participate in testing. Meanwhile, the main branch still consists mostly of players focused on ranking up or just playing for fun. There’s only a small group of us left who actually give feedback on bugs and gameplay issues.
I get frustrated sometimes too. Aside from a few lingering bugs, it feels like there’s nothing left for us to do except wait for the next patch, big or small, so we can look for new issues to report or give feedback on. I just wish there were another way to access the Experimental Branch besides referrals, being a top-tier bug hunter, or being hyper-active across every community platform.