TL;DR: Antec is going to be selling a Steam Deck competitive device, based on the Ayaneo Slide. The device has a slide up screen that reveals a keyboard, which is good because using desktop windows is much easier with a keyboard. However the device’s lowest estimated power draw at low/no load is 15w, meaning it will use comparable power to the deck running at max power. This means the battery life will probably be pretty rough when compared to the Deck. It will also likely have a much higher price point.
You’re right, of course. But there’s still a few games that don’t run on Steam Deck (looking at you, Henteko Doujin), that run fine in Windows. I’m able to play these games on my Ayn Loki Zero with Win 11 install, via Steam. Of course, I’m talking about playing indie shmups on a US $250 device, so I’m a bit of a niche case. So… situationally it’s a good-ish idea? For, like, three people? Not enough people to make a product worth selling, anyway.