Valve and Steam add no real value to the products they sell.

A small quibble, but this is wrong. They are acting as distribution/publishers/storefronts. Not every game developer can host secure digital downloads of their game any more then Id in the 1990's could produce all the copies of Doom/Wolf3d they were selling.

You can argue that the fees for their services are too high, but no one is forced to use them if they just want their game to be sold. For example Starsector (https://fractalsoftworks.com/) self-distributes, and doesn't require a store front installed on your pc, but apparently lots of other videogame developers can't do that.