Is there anything preventing a healthy competetive market for game stores on PC? Does Steam/Valve engage in behaviour that limits competition? Alternatives do exist - itch.io, GOG, Epic Game Store, and just putting an .exe file on your website.

If the market is not being artificially suppressed (I don't believe it is), and developer still think it's financially advantageous to pay Steam's fees, doesn't that indicate the fee is "correct"?