I think Switch has a different market (albeit a bigger one)than the Deck.

There is definitely market overlap with Steam Deck but I feel the Deck offers things that the Switch doesn't. In a similar vein, I think Steam Machine provides a kind of value that extends just beyond the console market. There are people who would not consider getting a console but would definitely consider getting a powerful and compact Mini PC with good gaming capabilities. Therein lies the greatest value of their offering.