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.

This 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.