I wish there was a way to know or accurately estimate what kind of cut is needed in order to pay all expenses and maintain a healthy profit margin. Based on the fact that Epic and Microsoft are pretty cutthroat I am guessing that 12% is the absolute minimum, with razor-thin margins or even straight-up losses. Maybe we'll get more information from data revealed during the various court cases.
Personally I don't care about Valve's profits at all, God knows they are printing money and they will continue to print money for the foreseeable future. What I do care about is the quality of service I receive with my purchase. I see the kind of effort and investment Epic puts into its service's development with its 12% cut and I get worried. All non-Valve services are awful, even those with a 30% cut. I shudder to think what kind of derelict pieces of shit they will be with a reduced one.
With the wallet cash cards business costing them a retail cut of 10 to 15%, I can't think they can go lower than 15. Wallet cards are big in emergent markets.
So if they are "strong-armed into giving a 12% cut, they would either need to cut some avenues (I can't see them foregoing Wallet cash cards, too big a market)
The 3rd party key market would fall really fast by two factors, too low margins with 12% and Valve cutting the free key generation as their first reaction.
Here is what "asshole/villain" Valve could do if they are strong-armed into giving 12%
In this scenario, I will theorize that Valve doesn't make the 12% cut globally but offers it to its partners. (A legal loophole to not get sued for monopolistic behavior. This "Offer" is not different than an exclusive agreement by other companies.
1. 12% cut
2. The agreement lasts 1 to 2 years, after that it goes back to 30% (with the current 25% and 20% revenue targets)
3. The game has to be available for at least 5 years after the agreement ends (so that the devs/pubs don't just pull the game afterward)
4. No free keys
5. The game can't be sold at stores that take more than 12%. This INCLUDES Consoles and mobile. (The whole number 5 would be clusterfuck, but hey it's an exclusive agreement
)
6. CDN and download costs above a certain threshold will be billed to the dev/pub
7. payment processing fees above a certain threshold will be billed to the dev/pub
8. If point 3 or 5 are broken, the dev/pub must repay the difference to the normal 30% cut
9. All steam API's and connections are free as always (to not fuck the customer)