1000x this.
When I grab the deck it's downtime mode for me now, keyboard/mouse time is work or side-project mode.
Mario Kart is also a funny example as it's one of the few racing games that makes no use of analog triggers for acceleration, so you really wouldn't miss much playing it on a keyboard.
The most comfortable and consistent gaming experience is still a regular stationary PC. But if you really want to play Civ5 on a train then sure the Steamdeck is there for you. I just never felt the need to game something that bad.
That would be playing console on an 80 inch screen from a couch.
I would have gotten a mini PC, but strangely enough the Ally was the cheapest steamOS-compatible option I could find.
My current obsession is Satisfactory.