it doesn't cost 30% to serve up the files and process some payments.

No, it doesn't. It also doesn't take $5 to make a cup of coffee, or $10 to make a plate of pasta, or whatever Netflix charges every month to serve up mundane low quality streaming video.

But unless you're proposing ending capitalism to fix the problems with valve's pricing model, there won't be any change to it any time soon.

The only thing that will get valve to have more competitive pricing for video games publishers is if they have actual competition that can siphon away games from their platform. It's not valve's fault that everyone else has made inferior products.

And there's nothing forcing you to publish on steam. If you don't think 30% is a fair exchange for handling file distribution and payments, you can handle your own file distribution and payments. Your game isn't forced to be on Steam.