I paid $350 canadian for a 64gb steam deck and paid another $100 canadian for a 1tb 2230 format ssd (thats only $80 now). I think the canadian dollar is slightly more valuable than aussie bucks right now but not double as valuable. 1 canadian dollar is $1.12 kangaroo bucks.
So your evaluation of the cost of the steam deck is just wrong. Its way cheaper than you imagine.
Also, valve has put literal years into Steam Input, which lets developers set up controller support, and also lets you load community sourced controller setups for your games. The Steam decks touchpads also let mouse driven games work pretty amazingly in a way that an xbox controller or switch can't.
You're just kind of wrong about the input situation. steam has basically the most sophisticated input software you can get and most of the time it just works, and when it doesn't you just load a community setup and play.
I'm not trying to hate on the steamdeck. I think it's super cool and would love to have one. But it's too expensive for me and I'm not sure they even ship it to my area. While the switch is super affordable and a just more out of the box works experience. I know every game I buy for the switch will work great on it, meanwhile I can expect most games I have on steam will not have great controller support or may not run well on the system so its a bit more of a "at your own risk" platform.