stone age development experience

simply not true. Stadia had full integration into MSVS in build and debug flows. Even 'lets show a build to management' flows there were better than Windows (i was in shock myself). And for long time during Covid Stadia builds were the easiest way to get playtests up and running at home.

But I agree with your other point that investing into porting and Vulkan renderers was a huge waste of dev resources.