So I was wondering what the proper way to fix this would be? Should this be made overrideable by a registry setting for certain games? Or should the GL check be changed? Or is that software emulated vertex blending patch needed to correctly fix the issue?
The correct fix is to implement a fixed function pipeline replacement shader and emulate vertex blending with vertex shaders. I have started such a replacement pipeline, but have paused it because it did not achive the intended results(performance improvements). This was about a year ago. Someone rebased it to wine git a few months ago, the results are in the wine-devel archies.
Note that my replacement pipeline does not yet implement vertex blending, but it is needed to add this emulation on top of it.