I see the handheld as a stepping stone. The big benefit to a console style device is a very small amount of hardware to target, whereas the PC market at large is a very large amount of hardware to target.
The handheld was just a market that didn't have much competition at the time. Which likely made it easy to justify it as a business decision for Valve.
Its all part of the stack. Every part of it was critical. Id say proton without the deck wouldnt have the same impact because there would be nothing to create the groundswell of linux adoption for gaming
