Yeah, it definitely needs trackpads that are easy to reach in order to be a Steam Deck controller. (And I'm saying "easy to each" because the awkwardly placed Playstation touchpad doesn't count.)
I'm curious about this part, though:
Gyro in the "Steam mode". With the sticks having a touch sensor too.
That sounds like an advantage over a Playstation or Switch controller. I'm guessing that means you could enable the gyro just by touching the analog stick, without having to press a button. That's like what most people did on the Steam controller, where the gyro would enable when you touched the trackpad.