No indie game developer that has been around for a while would say this. A 30% cut is way less than anything else that came before it.
Steam also allows you to sell Steam keys from wherever, and you get to keep 100% of that. This is how Humble Bundle works.
When you release on Steam, you also get free exposure at first, which is basically free ads. You would otherwise pay several thousands of dollars for that.
So in any sense, Steam worked to get that 30%, and there is no serious indie game developer that is arguing with that.