If you don't mind being plugged in then the better specs can be used without having to worry about the battery, some options have a bigger screen and better resolution, some options have a bigger battery than the Deck (double the Deck's battery in the Ally X) , as I mentioned the trackpad isn't essential to everyone (if you're always playing games with controllers anyway, you're probably not playing RTS or city builders)...

It's ok for the Deck to not be the only option people should consider, it's nice of Valve to develop stuff, it's a good thing that they have competitors.