In my mind, there are two asymmetries.
* Microsoft v. Users
and
* Casey's network v. a 3-4 man open source team within microsoft
I don't disagree that the former is abusive.
However, it's my contention that this incident is primarily about the latter.
Casey, rightly, already had some pent up rage about the former asymmetry as well.
But it was a human manager/dev? within that small team, not Microsoft writ large, that got defensive about the software he was responsible for.
I believe I'd feel embarrassed and defensive too if something I'd worked on turned out to be flawed in a painfully obvious way. I can understand avoiding the grim truth by denying that the problem has truly been solved by ~700 lines of C.
Something else that I'll note here is that the vast majority of "Your software is too slow, Here's how to fix it, I could do it in a weekend, and by the way this whole problem space is actually super simple." tickets do not end up realizing software speedups. Without proper context, they just sounds patronizing, making the argument easier to dismiss.
It's also important to keep in mind the vast asymmetry here. When Microsoft deploys problematic software, even a relatively minor problem will be responsible for many man-hours of frustration and wasted time. Far more man-hours than are ruined when a few developers have bad things said about them online. One doesn't excuse the other, but you can't ignore one of the harms simply because it's more diffuse.