This is such a bizarre lawsuit. I had to pull up the actual filing to make sure I wasn't missing something.
Specifically, the PCR contends that Valve has abused its dominant position by:
(a) imposing Platform Parity Obligations (“PPOs”) that prohibit publishers, which market PC Games, from selling Products through other distribution channels on better terms than the same Products are available on Steam
This is only true if you're selling Steam product keys, which I feel just makes good sense. You're still selling something that's on Valve's platform, so you need to adhere to Valve's rules. You can offer a non-steam copy under any terms you like.
(b) restricting the ability of users to purchase Add-on Content for games purchased on Steam through other distribution channels (a ‘tying’ or ‘anti-steering’ infringement)
...is there any platform where this is not the case for paid content? I guess for anything that has additional content available on GoG this is technically true by virtue of it lacking DRM, but where else would you even buy it in that case? Is there some other DRM-free platform from which I can buy Blood and Wine and drop it into my GoG version of Witcher III?
(c) charging publishers unfair and excessive commission rates for distributing the Products (collectively the “Infringing Conduct”).
The question of whether Valve's 30% is "fair" or not has been beaten to death already but it is funny to me how it was basically the industry standard right up until people started gunning for bigger pieces of the PC gaming pie and started undercutting Valve.