Why won't it play GTA5, Cyberpunk or CoD? How can you be so sure of that? Have information we don't? If your angle is the DRM side, Valve is working on it. On the other hand, you could just install Windows and play them there.
Also, while portable emulators have been a thing for a while, they aren't full fledged portable PCs that, well, give you much more than just one thing; this is to say, the Steam Deck is not a "one trick pony" like Consoles and/or Emulators.
If it's not for you, that's fine. That doesn't mean this product is a bad idea or that it won't succeed. Your main argument is Valve's support. Do you even own any Valve hardware?
Regards.
Many portable PCs have come out over the years that weren’t laptop shaped. None of them ever succeeded. As soon as you plug a keyboard into it you’ve already lost. Running full blown windows 10 on it so you can install Origin and Battle Net seems laughably silly.
I still don’t want yet another emulator handheld even if it is a “full fledged PC”. I have a raspberry pi with plenty of emulators on it which is loaded with 10,000 games across 100 emulated systems, is as portable as I ever really need, and which, honestly, I’ve touched maybe twice in the three years since I bought it and installed all the roms ever on it.
If (a big if) they do get around the DRM limitations and get it to run COD on Linux, it won’t be pretty. The graphics performance will put a lot of casual gamers off, even at 720p and assuming everything works flawlessly on it.