Everyone is saying you don't know what you're talking about, but you're obviously right. They're one of the most profitable companies per employee in the world. Saying they could take a smaller cut and still be profitable is obvious to anyone who doesn't have their head in the sand.
Valve is using their market dominance to force price parity too. This is an ongoing case, but all the documents seem to indicate this is true. For all the "Valve can't do anything wrong" people, wouldn't you rather pay less for games? If another market is allowed to sell a game for 10% less, isn't that better for you? Maybe Valve sees this and cuts their share to drop 10% too, but isn't that even better? Why are you so insistent on arguing against your own best interest.
Yeah, 30% is standard. Who the fuck cares? Don't you want it to be lower? Do you know how that's lowered? It's by other stores competing on that cut. They aren't allowed to (on the consumer end) though. Epic does on the developer end, but Valve prevents them from giving consumers a cut.