Not always, they only started to offer Linux support after Steam, and even then it’s just a very small part of their catalog and none of their own games/products, so I think it’s fair to say they don’t offer Linux support but sell some products that do.
I agree with most of what you said, I don’t think the price is as high as people make it out to be, but:
Cheapest version of the Steam Deck is still cheaper for very comparable hardware, and while generations don’t align I think the Deck is closer to the Switch 2 than to the switch 1, and a Deck 2 would be miles ahead of a switch 2.