It's totally okay to like Valve or Steam as gamer. As fellow gamers I totally agree with you.
Just next time when you wonder why you favorite studio went bankrupt or why you niche genre game never got a sequel this is why: because some monopoly took 50% of their profit.
30% for this is high, but then there is also the discoverability. Which I think does beat google by long way. So they probably would not have sold as many copies without popular platform.
And I am absolutely certain that some developers would exploit this in someway.
12+ years ago if you released on Steam it was a big deal and platform provided traffic to everyone, but today it's flooded with games so basically you're on your own.
The only thing that allow Valve to charge this much is network effect. They are not vendor-locked platform like App Store, but they do have nearly monopoly on PC.