They definitely each have their own strengths and weaknesses, if I had to pick a winner, I'm going with Steam Deck, you just can't compete with their controller API and the Deck's assortment of input options; that alone makes everything else obsolete.
Raw horsepower(Rog v Deck) is a meaningless metric; Using the Rog is like driving a 911 without tires, just rims; you literally can't control it.
I almost always play with split joycons if I'm docked. I recently got the Nyxi wizard controller, which is like a split GameCube wavebird, and it's way more comfortable in handheld. I wish the buttons were higher quality but otherwise I'm digging it.