OK, I'm going to try to explain this to you in one post. I don't care enough about either side of the argument to put any more effort than that. You may be right in assuming 343 did something wrong. Lil Frier may be right in assuming 343 acted reasonably. I don't really care. You are, however, completely wrong in dismissing his side of the argument.
First, a couple of premises.
1) Halo: MCC matchmaking was not completely broken. Sometimes it worked, other times it took a really long ass time to work.
2) There is no indication that the matchmaking issue was a known problem at launch. Maybe they knew about, but there's no report suggesting that they did, which to me makes it more than likely that they did not. Maybe they did not know about it because the bug in the code was something that didn't show up in their tests. Given fact #1, that matchmaking was never completely broken, it is entirely possible that matchmaking passed all the tests they threw at it during testing.
3) There is no proof that they would have discovered it in a reasonable amount of time with further testing. There is no proof that 343 was not diligent in the testing they did for matchmaking. Lots of problems lurk in the shadows pre-release that are difficult to impossible to discover in pre-release conditions. If you truly have been in software development for 10 years, you would know this. What if the issue was that the matchmaking algorithm goes bork when facing an extremely high load of requests? What if the issue is caused by some unique combination of matchmaking requests? Or from some unexpected combination of Halo score/level, matchmaking request type, connection type, etc.? It would be very easy to miss this during testing, and there's a very good chance it would NEVER be caught even if you went through YEARS of testing.
The issue at the heart of the matter is: was it reasonable for 343 to release Halo: MCC given the information known to them at release? Nobody here has an answer to that because nobody here knows what 343 knew at release and nobody here knows the details regarding how exactly matchmaking was broken.
Also, as to open beta testing. Yes, it is usually a superior method of testing software. However, it's also not a guarantee. It's entirely possible that the bug wouldn't have surfaced even in open beta if it were related to a certain load level for matchmaking requests that is > the open beta pool and < release pool. Also, there's lots of good (profit related) reasons not to open beta test. Not all software is tested in open beta and not all software should be tested in an open beta. Maybe the rationale was that they thought that since it the game was a re-release and half the value is the nostalgia, open beta would cut into sales figures as people got the nostalgia for free during open beta and did not buy the final product. Who knows.