From my 12y old kids perspective:
The switch 2 plays fortnite and Mario kart. The steamdeck doesn't.
There is no difficult choice for him.
He doesn't give a fuck about anything else. Neither do his friends.
Not to argue about the privacy issue, but aren't there better options than a towel? Get a phone without camera? Get one of those phones with physical switches for sensors? Get graphene OS and don't install anything but signal? I feel the towel wrapping is not the best solution for your privacy issue.
A 10usd Chinese knockoff Bluetooth controller works well enough for multi-player. The true little brother experience is to play with the shitty controller.
For the steam deck, you'd have to buy 2 controllers (potentially both shitty), so the benefit for the switch is still there.