Okay, I'll address those in random order:
1) Based on my involvement in bug tracker in BF4 and 1, there is no "medium" severity - there is Trivial, Minor, Major and Block (there used to be Crash too) - Block is applied when it's impossible to play singleplayer, multiplayer or the game in general, while Major is applied for cases that compromise the ability to properly play a bigger part of the game. For example, in context of planes, a Major-level bug would, at minimum, be the complete inability to use one of planes. Bugs like one here generally were marked with Minor severity. Should they still be found regardless? Probably, but things will slip by. QA will not get nearly as much coverage on its own as playerbase will, the difference in sample sizes pretty much is a couple of orders of magnitude here.
2) Volunteering here has nothing to do with defending anything - it's an extremely common misconception that, while understandable, has little to do with reality. I've criticized things a fair number of times myself despite being the Hero here and moderating in multiple other places. Being in one of those positions doesn't mean that you have to act positive about everything even if things are on fire. Just like anyone else, if you don't like something, you say it (politely, of course). Also, there was no talking down here. Unfortunately, things often have to be put that way, as, once again, a lot of people actually believe that fixing things is something that can be done basically instantly and with no effort. Yes, some people have an understanding of how things work, but many do not, and that's why the reply was straight to the point. And just finding the bug actually is a fairly minor step in context of fixing it. If reliable reproduction steps are not established, fix won't happen... and figuring reproduction steps out is a way tougher task out of two. Think revive bug in BF1. Common, but as reproduction steps were extremely difficult to find, it couldn't be fixed for a long time.
3) On hotfixes, I believe there has been a grand total of one of those over last couple of Battlefields. While I obviously have no knowledge of why it's that way, I would not really take that route into consideration. Not a fan of that and I have my guesses on why it is that way (most likely the likelihood of hotfix causing damage to actual big patch and/or a matter of internal 2-week patch test period), but that's the way DICE has always operated. What I do know is that December 4th patch has been locked down two days ago and it's currently being tested (source: https://twitter.com/JaqubAjmal/status/1066023990450417671).