The above article estimates the PC gaming industry sold around 32.3 billion in 2017, although from [0]:
> If you throw out revenue for packaged retail titles and browser games, that leaves the dedicated digital PC game business with a total value of $23.9 billion – and that number includes DLC, which the Steam estimate does not.
> If the numbers are right, that means Valve own at least 18% of their specific market
This is by no means exact, but 18% for PC gaming is huge and, given that these are global numbers, probably doesn't account for the PC games market in China.