The thing is when people put games on Steam they account for the fee that they take. So in a sort of way the lawsuit is right, Valve are effectively causing players to get overcharged for games.
But if I put the same game on both Steam and GoG And make the gog one 20% cheaper, I still get more sales on the Steam page. If I only have it on GOG people actually complain even when you point out that it’s cheaper that way.
So Valve are causing players to get overcharged but players are forcing publishers to put their games on Steam. So players are causing players to get overcharged, so what can you do?