I wasn't making an argument that Apple isn't doing anything illegal, but I think it's not credible to argue as @herf did that "there has been no market discovery of prices due to exclusivity."

The market for Android and Windows app stores has settled on exactly the same rates as iOS apps, which is exactly same rate as game-console platforms that have only one exclusive store. 30%, across the board.

Android alone is sufficient evidence that sideloading doesn't force the dominant app store (Google) to lower its rates to compete.