Fortnite changed steam's dominance. Epic games is buying out a lot of games to offer on their store and they have the cash to burn on it. Who knows where all the fortnite fans will be in 5yrs, epic or steam.
Hard to blame them for a stance of "you can't use our storefront to advertise other storefronts" though.
Epic is doing the things it is doing precisely because Steam is so ludicrously dominant. I'd argue that they haven't been successful at usurping that dominance yet. They are still very much playing catch-up.
They prefer their churn and burn, buying out games and giving them for reduced prices. It makes little sense unless it is seen as a very long term play.
Valve own marketing material doesn't count.
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.