So 30% is some magic number where platforms suddenly become profitable with improvements. Yeah I don't know, I'm gonna need to see some source about the costs. In my armature opinion it would be enough with 2-5% cut to still be profitable with improvements.
The point is that neither you nor me know the economics of platforms. But I'm certain that 30% is not some magic number and that there is a lot of profit until you reach 30%.
Half your post is literally just projecting things into my post i didn't even wrote lol, but let's go with that:
The fact that the epic store needs to charge additional fees to their 12% cut in multiple countries proves that 12% isn't enough to actually cover their costs in these regions, as said by the CEO of Epic himself:
Apart from that, most popular payment methods (Credit Cards, Paypal) already charge between 2 and 5% per transaction:
https://www.paypal.com/us/brc/article/understanding-merchant-credit-card-processing-fees
https://www.merchantmaverick.com/the-complete-guide-to-credit-card-processing-rates-and-fees/
The idea of operating an entire global backend and continously developing the platform profitably at 2-5% is nothing but a complete pipedream because that'd make you lossleading.
Then you have epic saying they won't have forums like steam does because "they want to make it optional for devs, so those that want can use steam/discord/reddit) which is an obvious lie if you look at how they say they want to handle user reviews, where it'll be an opt-in feature for the devs.
If it would be about options they would just implement forums as a feature and give the devs a toggle like they'll do for userreviews, but they won't, because it's factually not about options, it's about cutting costs.
To reitarete on my initial post: I'm not saying it's impossible to go beneath 30% at all, i'm saying epics 12% make it impossible for epic to ever be on par with other platforms because they literally won't be able to afford it with their incredibly razor-thin margins.