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.
I think the biggest single factor they point out is the software side of things, in combination with the other factors such as hardware/price. Although the Deck ain’t beefy, it’s got enough juice to do a lot at a battery rate that isn’t terribly abysmal, especially for lighter indie titles and emulation.
The other factor here is outside support and adoption. There are tons of options for third party customization, such as skins, buttons, pads, cases, etc. Not saying these don’t exist for the competition, just not at the same scale. Kind of like finding support for a niche android phone versus an iPhone.