Of the ones you listed, consistency is the big downside for me. It seems like there's multiple options for everything in the Linux ecosystem. From the beginner questions (e.g., which distro), to the nerdy questions (e.g., systemd vs sysvinit), to the ones in between (e.g., vim vs emacs). I sometimes wonder if GNU Herd would have been better at this, since everything would be designed by the GNU folks for one unified ecosystem.
I don't think Valve will fix it TBH. They only care about Linux UX on their hardware, i.e. Steam Deck. I don't see why they would fund things like KDE, or features in the kernel beyond the ones that they need for their products to work. (Not that I think they're assholes for this; just that it's unfortunate)