Steam Deck is an x64-based PC running Arch Linux with FOSS Mesa drivers, which are shared among all modern AMD GPUs. There's extra wrinkles with Nvidia GPUs, but their proprietary driver is the Windows driver with a bunch of kludges to get it to work on Linux and if you're using Vulkan then it's mostly the same code paths. It's also improved greatly in the past couple years.
You're right about native Linux binaries, but the rub is that you don't need to create generic binaries, there's a bunch of options that use containers to deal with environmental permutations and given the Linux version of Planetary Annihilation uses the Steam Linux Runtime environment, you know this.
It is funny that supporting Linux is as easy as providing a win32 binary, but it's not a joke. This is the case because it works.
I think your experience is a little out of date, or you've somehow been missing what's been happening over the last half decade, because in practice gaming on Linux is now absolutely fantastic. Not just on Steam Deck, as since Valve is using the same general software stack that every other distro uses, all the improvements they've made have permeated out to the rest of the ecosystem. On my CachyOS PC with an RTX 3090, the only games that consistently give me problems anymore are titles that ship with kernel-level anti-cheat. Otherwise when I buy something from Steam I simply assume that it'll work.
Steam Deck sales have actually softened quite a bit over the last couple of years, all this recent explosive growth has been driven by desktop users.
