You could, but what makes Steam Deck special is that it's SteamOS is built specifically for that hardware, enabling functions you wouldn't normally see in gaming PC hardware.
The main benefits of SteamOS proper is that it is a distro that takes a very "windows" like approach to papering over/obfuscating a lot of the internals. And the main feature it has over the competition is that, because Valve have so much control over the OS, the gamepad controls of desktop work a lot better.
But I want to say Aya also provide that, but in Windows? I know either they or GPD do that because that was a big reason I didn't want to GET (probably) an aya neo: Not super huge on so much closed source software provided by a random company having that much control over my OS.
And... I am still not super huge on Valve having that much power. But I "trust" them more.
But curious if am missing something.
And I'll add on. This should not need to be provided by the vendor. On Windows, they have pretty strong tablet/touch screen support which goes a long way with keyboard popups and the like. Linux needs to step up its game and make sure that gamepads can be treated as first class citizens input wise and distros/workspaces need to make keyboard popups in a similar state.
At least one of the main features is seamless suspend/resume. Not sure what the state of that is on Windows but I've seen a lot of people mention that SD feature specifically.
And with VRR in general it matters a lot less if you have a steady framerate. Pretty much my only complaint with the steam deck hardware is that it is not a VRR display. Much like with dlss/fsr, freesync/gsync is perfect for when you are running an emulator with wild performance swings or at the limits of your hardware.
And, back in the day, you could do weird stuff with telling windows that your monitor had a different refresh rate to do this but it was far from pretty and prone to strange behavior.
Small nitpick. I'm not sure why you don't like the idea of the vendor having stuff installed on hardware they make, to ensure it functions optimally. Like, on a primary compute device, sure, be picky about the OS. But this is a game platform. Nobody gives a shit that Nintendo makes their own OS for their hardware, why does anyone care how the Steam Deck does it's thing?
I actually have a lot of issues with the walled gardens the console makers sell. That doesn't stop me from using it, but I should not need to wait for Sony to "add support" for basic HDMI standard features like VRR and question why the only tvs that support that are their own.
In a perfect world? Standard, preferably open source, libraries and tools for anything possible with "ease of use" and the like provided through the same package managers and management tools that allow IT departments to manage/monitor deployed systems. This greatly reduces the need to hope that Microsoft add discord support to the xbox or that nintendo... understands what an internet is. And it greatly reduces OS development/overhead for the consoles because... it isn't like people are buying playstations for the... I can't even think of anything unique to the OS that isn't purely UI/UX.
Fair enough! I mean, that would be really nice tbh. Also it makes me realize that consoles only exist for DRM, which is sucky. Granted, I stopped buying consoles almost a decade ago, so I never stopped to think about it.
The difference is that if the device comes with Steam OS, then it's ready to go out of the box and you're assured the hardware has good Linux support.
If it's originally a Windows device then you may have to jump through additional hoops to get everything working. Also you'll have to deal with allowing other OS's in the BIOS if it's locked.
Also you've paid Microsoft for a license you won't use.
The flip side is that there's work to make a native Steam OS build for 3rd party portable devices:
I used the steam deck as a daily driver between laptops. It was good enough to the point that if I had a decent mobile monitor, I would consider it exclusively for a travel rig.
I am looking specifically for a single device for travelling with. But the built in controllers of the Steamdeck are just a little too goofy for me to give it much serious consideration.
Outside of the better gpu, the one advantage the other devices have is emulation. Steamdeck sits on the edge of performance for some of the harder to emulate devices heavy titles (PS3, Switch). The ones using Ryzen 3/4 would trivially handle emulation better than the Steamdecks CPU, which uses Ryzen 1+ (part of the reason why its low cost)
I've got an external monitor and my full keyboard and mouse with a dock and my steam deck. I can set up anywhere with a desk and game, program, whatever. I've found very little that it can't handle.
I'm using this portable monitor but it is kind of finicky, and I worry it'll break easily. It's the biggest one I could find at a reasonable price, and happens to fit my backpack.
I've used it with my 3440x1440 freesync monitor at home, and it works as well, but like anything, whether you can game at that resolution is very dependant on the specific game and settings you use.
I'll add, because the deck doesn't have thunderbolt, plan on using HDMI instead of type c.
It's possible you can find a type c (non-thunderbolt) dock that supports powering and driving a monitor over type c along with the deck, but I wasn't able to find one.