Steam is probably the only store that does something to deserve the 30%.
Was, these days, maybe 15 to 20% max. As developer if you dont receive at least some decent traffic base from a fair algoritm, it doesn't really matter. The rest of features are useless.
For example humblebundle widget, it gives you 90%. For that it provides with the tools to manage ur builds, upload keys, library for user downloads and stats. No traffic!
Steam gives u some traffic on launch, but without huge PR and/or a 30-50k wish lists, low chance to get anything out of it, and now with the latest algorithm, it basically killed indies, that are under 10k to 30k copies sold. So why give 30% then? Well cause fuck you!
As a user Steam its ok, i use it, not so much, since i despise always online crap so i play offline. As indie developer if you are one, without much back/investments, you will hate Steam and their incompetence (lack of curation, adding algorithms without proper tests, that can cut your income by 70% for some months, etc).
So these days instead of adding proper curation, they added an algorithm with the title "helping indies!" ay lmao ! that basically destroyed the sales, wishlists by 70-90% for almost all indie games without huge marketing under 10k-30k sales. Steam is great!
The future for a few indies that will survive, is either sell big on steam by luck/skill and PR, or build slowly and smartly a community on your site, and use these stupid stores as secondary or tertiary income. Good games that did that, but its quite hard: Starsector, Rimworld and others.
Meh...