There are plenty of supposed Steam Deck killers available in the portable gaming space, from the Asus ROG Ally to the Lenovo Legion Go and all the Ayaneo and ONEXPLAYER devices in between. But none of them have managed to outright slay the dragon that is the mighty Steam Deck yet.
Why don’t tech reviewers every talk about gamescope? Gaming on PCs has always been finicky because PCs have to serve so many use cases at once and games often have to compete for resources. Gamescope completely circumvents all of this overhead by being solely meant for the purpose of gaming. It’s the closest you can get to a “PC Console”. Third parties can never make something like gamescope for Windows, Microsoft themselves would have to ship it and maintain it.
Because tech reviewers only read spec sheets and call it a day. They usually get the product for free and use it for a day or two, which is not nearly enough time to make an actual review of the product.