In the Windows team (back before the test org was decimated) I saw the described "class divide". Anybody who was good enough would switch from SDET to SDE [disclaimer: obviously there were some isolated exceptions]. The test team produced reams of crappy test frameworks, each of which seemed like a "proving project" for its creators to show they could be competent SDEs. After the Great Decimation my dev team took ownership of many such frameworks and it was a total boondoggle; we wasted years trying (and mostly failing) to sort through the crappy test code.
replyThis was all unfortunate, and I agree in principle with having a separate test org, but in Windows the culture unfortunately seemed to be built around testers as second-class software developers.
I spent most of my time working on Visual Studio (in the Boston time frame) so we got to interact with pretty much every team. I absolutely hated interacting with the Windows team. Everything was a fight for no reason.
replyAs I said above, everyone has their own experiences but the QA folks I worked with at MS were fantastic.
Not sure if you're aware but Dave Plumber now has a really good YT channel [0] where he talks about MS back in those days. It's a fun walk down memory lane.