Sure but it's also a badly done lawsuit for that. It's a class action of Valves customers when the percentage almost entirely impacts developers and publishers not customers. If this was really about Valves cut it would be a class action by developers. The reasons it isn't are that that's a much smaller group, consumer protections don't apply to them so that would be a much harder case to win, and finally they would struggle to find developers willing to join that lawsuit. There's also the slight problem that the 30% cut is the industry standard. Both Apple and Google take a similar cut. I'm not sure who originated that as the standard, could go all the way back to brick and mortar stores or it might have originated with one of the games consoles, but Epic is actually the odd one out in this case not Valve.

As someone else pointed out there are things that Valve could be better about, things like lootboxes in some games or the frankly predatory CS item markets. The issue of course is that none of that is actually illegal even if it is anti-consumer. It would also be nice if Steam had some actual competition, but there isn't anything Valve can do about that, rather it's everyone else that needs to get on Valves level.