I don't believe that's the case anymore. Newer console generations have moved on from exotic ISAs and the like towards using a lot of off-the-shelf parts for smartphones or PCs. The Switch, for instance, has been sold at a profit from day one [1].
[1] https://web.archive.org/web/20170131084504/https://www.bloom...
A big part of differentiating a console from a PC is building an operating system that prioritizes the game process uber alles. It's not just a fancy window manager slapped onto a commodity PC. Even the original Xbox had a lot of custom OS work done to it, stuff that would eventually serve as the test bed for developments in DirectX.
Does Valve even have any operating system developers? I thought their core dev body was mainly focused on screwing modders and getting kids addicted to slot machines.