On PC, Microsoft takes a 0% cut of apps distributed through it's store and 12% of games, so EGS isn't really the outlier there, but regardless 30% being average in an existing anti-competitive industry doesn't really prove anything about whether or not it's a fair cost. That can easily be oligopoly collusion / price signalling which happens all the time.

Console makers like Microsoft and Sony are also funding building the hardware and maintaining the platforms since they lose money on up front hardware sales. I'm not saying I agree that this should be a legal business model, but they have more of an argument for charging 30%.

And regardless of all of that, when I'm talking about a fair price, I'm talking about a fair price in an economic sense, as in, does Valve provide more back to the economy then money they take out of it, or are they rent seeking? Given that Valve made more revenue per employee than literally any other tech company (pushing $1million/employee/year), all during a period where their employees literally were allowed to work on whatever personal projects they wanted (virtually none of which went anywhere or made Valve any money). In that context, I can't see their fees as anything other than rent seeking. Yes make a profit, yes pay your employees well, keep a nice cushion, and invest in R&D, but Valve has been able to afford to do all of that and just burn / hoard cash at a ridiculous rate, all money that would be going to the actual game designers and developers if we had competitive markets.