Yes, I agree that 30% is a lot. But let's look from another perspective: If a developer, for ease of calculation, sells a game for 30$ on Steam, he receives 20$. If he sells it on a competitive platform with 5% cut (that's 6x less than Steam) he gets 27$.

However, Steam is way bigger, and if a developer can sell the same game more times on Steam (33% more times to be exact), he breaks even.

More people to buy = more people to play = bigger player base => more people buy it. It is a poaitive feedback loop.

I am not arguing that 30% is good, all I am saying is I understand that Steam has to take a big cut to pay for the features it provides for "free" alongside the usual game content (cloud saves, community, workshop, utems, etc.).

Do you think any indie developer has the means to achieve a lower cost to distribution and promotion if they try to sell and support the game themselves?

Valve solves many problems for developers and these problems aren't imaginary and free to resolve.

Not saying 30% is justified for all games, but if you want a quality title it's going to cost more than just development. Since the Unity debacle we've seen some developers even say openly that costs of promotion and support dwarf costs of development.