The amount of bugs in UEFI of new motherboards shocks me. Bugs are all over the place; sometimes I change an option in Setup only to find out it's disabled after reboot, and switching the option ON for the 2nd time works. Or, on my motherboard boot menu is bugged. To boot my Windows disk, I have to choose 'Switch to English' menu entry. I'm afraid to clear EFI vars because currently at least it works, who knows what'll happen when I clear EFI vars.

This really discourages me from buying new hardware.

I feel your pain but it really doesn't shock me at all. Closed source blackbox firmware made mainly by hardware vendors? What could possibly go wrong. Even AMD and Intel are very hit-or-miss with the quality of the software they produce, can you imagine the random mobo maker? Have a look at some of the vendor-maintained forks of u-boot and Linux (whose code they have to publish because the GPL) and see how many bugs you can find.

Meanwhile the software embedded in these boards becomes more and more complex with basically a full blown embedded OS, graphical interface etc...

Software shops have a hard enough time writing robust software these days, ASRock probably has a team of a dozen or so glorified interns copy-pasting from stack overflow (or worse, contracting third parties do to it). I'm exaggerating a bit of course but not by a massive amount from my personal experience working with hardware shops.