I have experienced it way to many, but i also play a lot... I think in total about 2-3% of the matches or something like that.
But i also have seen multiple streamers who got that problem, even the grassroots streamers during a playdate (those are supposed to promote MCC...).
This week it happened to me in a Firefight game (never had that happen before..) and even that got me a ban, even though you can quit banfree from firefight....
Perhaps it also depends on where you live? People closer to the halo-servers have lower ping, so they have less chance of being kicked from entering a match? For what i see most people complaining from these bugs are non-US players, those live farther from the servers. Perhaps that's part of the issue?
And even if you live in your own tunnel and just put up strawmans that no-one would have those problems (enough evidence otherwise, but okay...): why hasn't the harsher bans worked? The number of quits is higher now, the number of AFK'ers is higher now and the playerbase is lower now. Why hasn't it worked?
The answer is very simple: for the people who do quit often (and of course those exist) there is a very simple way to get around bans. As long as you can create a smurfaccount in much less time than even the first ban is, it will not affect them. That is also why you see a lot of new accounts of experienced players. The problem is that that messes up the matchmaking system (because that still seems them as 'noobs') and create more one-sided matches.
And something else (if you guys are allowed to use strawman, so can we): i am curious how come you experience that much quitters to begin with? I see quitters very reguraly, but way not as often as you guys claim. Most of my matches don't have quitters. So how do you have them almost always as you claim? What makes it that people don't want to play with you guys, while others don't have that problem as often? Are you that toxic during matches?