We have to start somewhere, don't we? Nixxes, as well as many other developers, are still learning the rope of DX12. They now have to deal with a lot more heavy lifting stuff that drivers used to do for them. As far as I remember, DX11 early games were kind of the same. Not every dev is as proficient as ID Software.
Regarding visual improvements, I think now that we are in a phase in which technical advancements, despite being more and more complicated, are not as easy to wow us as they were before, plus the difficulty to make everything work, it makes sense that they will focus more on the performance side of things.
Things will pick up, in terms of visual and performance, obviously. I just hope it's sooner rather than later.
Regarding this patch, specifically, it messes up my shadows, making it flicker in a lot of places.
Back to DX11 it is.