Valve can do things like this because they have a huge stable of some of the best and most experienced C++ programmers on earth, (and pretty much all SWEs on staff are expected to be at least fluent).
World class culture and compensation will do that for you.
I'm pretty sure they outsource/fund a fairly large amount of the work, the article mentions Igalia & from memory Codeweavers are largely responsible for Proton.
Valve itself is a pretty small shop. Although their own efforts & funding absolutely should be praised.
> I'm pretty sure they outsource/fund a fairly large amount of the work, the article mentions Igalia & from memory Codeweavers are largely responsible for Proton.
Userspace stuff for sure. But the drivers are mostly Valve.
World class culture and compensation will do that for you.