Hmmmm. Most of the arguments seem to claim you prefer something that is also a PC. But the Deck is ALSO a PC. Just one running Linux. But exit Steam, you have a full KDE Desktop by default. It's pretty much no effort install LibreOffice, and I'd assume it comes with a browser such as Firefox (though again, no effort to install it from the Software store). I believe it can run emulators such as Mednafen and Flycast no problem, these days the difference Win/Linux for emulation ain't that big, some had some leeway initially on Linux first.
With all this I mean, if you have your mind made, sure go ahead and buy whichever will satisfy you best. But you can just as well plug a keyboard/mouse on the deck, and hook it to a monitor with any USB dongle. Talking peripherals, and emulators, and most of the software, both should behave the same. So it's mostly whether you prefer the extra beef/power, the extra resolution, or some other options of the OneXplayer within the hardware itself, but not so much software IMHO.