I think there's something to be said between mobile app stores and what Valve offers through Steam though.

There's an argument to be made that yes, developers are functionally giving up an entry fee to Steam's userbase, but Steam also does run a very compelling platform. If it was just a storefront, I'd agree about rent seeking. But you get a pretty elaborate set of features that are legitimately what sets Steam apart from other stores:

• Steam community forums
• News feeds to make publishing patch notes easier
• Steam workshop for easy integration of community content
• A robust social network, with integration into the game for an easy means of inviting, hosting and joining games to meet parity with Consoles
• Steam's whole CDN/versioning depot
• a swath of marketing tools, Proton for multi-platform compatibility, etc.

For both its users and the sellers, Steam is a consistently improving platform. I think they've made some less great decisions over the years, or fail to enforce their own guidelines, but largely they continue to innovate and make it clear there's an interest in making it as complete and accessible am experience as possible.

To your second point, agreed. I despise the loot boxes and I think Valve is pulling some horseshit there. There's also no forgetting they had virtually no customer support for longer than they've had it. Refunds weren't even an option until 2015, and only came about as the result of multiple consumer rights suits. To their credit, they've made a point of doing that as well as they can too, but I still think there's room for improvement.

Nintendo, Sony, Microsoft, Google and Apple all take 30% to the point that it is accepted as the standard market rate. Epic points at Valve following the same standard and says they are greedy and now everyone parrots the Valve is bad claim. I'm sorry but I never bought this argument Maybe we should claim it's a problem with the industry as a whole instead of pointing to just one company following what others have been charging.

Valve is the least shitty option in a sea of garbage. If you find an oasis in the desert, do you complain that the water isn't cold? Someone could do better, yes; but they haven't.

Google and Apple both take 30% on everything, but that recently changed it to 15% for a developer's first 1million dollars, and for subscriptions.

Valve are getting 20-30% of every sale. Other marketplaces - notably Google and Apple - are rightfully despised for this level of rent seeking

The contention is that you're using Epic's dishonest framing of this argument. Retail fees are not rent seeking, and the only "despising" of Google and Apple came from Epic themselves because they did not want to get any less than all of their MTX money from Fortnite on mobile.

The 30% cut is the standard retail fee. It's the standard for all storefronts except for two: EGS and Microsoft.