It seems a bit like an unforced error to be dumping Linux a few months before Steam's new Linux-based Steam Link is released.
It's definitely an arms race, and the experience is getting worse and worse for customers (including software developers). I don't know if the average user notices these things or not. Valve is trying to not get caught in the crossfire here, and to have some recourse when inevitably MS wants 30% to allow steam to run natively in Windows. In the meantime they also have built a strong reputation among nerds like us, mostly as a byproduct.
But the parent did indeed mean the Deck.
Even assuming Steam Deck (which is what I think you really meant) is an absolutely roaring constant success then they still realistically have a couple of years before it'd really be a significant chunk anyways. That's ignoring the whole premise of their other development, Proton, which is about running the Windows games on such systems anyways.