I think it's important to understand that Casey is not exactly a "game developer" in the classic, broad sense of the word. Casey makes middleware, game tools, (engines) and such. That's his background.
And within that context what Casey does on stream sort of makes sense.
On the other hand, if you're primarily interested in "making games", most of the stuff on stream will appear like constant sidetracking, always opting to work on mainly irrelevant* technical stuff instead of doing gameplay programming or moving game to a more shippable state.
kewp
Nowadays the problem is creating a code base that runs on most platforms, is flexible and performant and not a nightmare to debug.
I believe neither of these things have been a real problem for gamedevs for at least a decade.
SDL, glfw and similar cross platform libs and tools have been out for a long time now.
Combine that with a conservative version of openGL and you are ready to go.
Dragging performance below 10ms per frame takes real talent irregardless if you use C/C++ or C# or Java or any other language.
And if you get a real performance hit, it's probably swaying to far off the "fast-path" of OpenGL.
Java with libgdx (LWJGL), or C# with MonoGame/OpenTK makes cross platform gamedev effortless. Neither are they engines which push upon you their abstractions or workflows.
It's never been this easy to make games as it is now. At least from a technical point of view.