Epic positioned the cut as the defining element of their platform. Not because it was meant to be, but because that cut was what Epic had available to them to rhetorically justify their intrusion into a space they're interested in only as a new revenue stream for themselves. Epic wants Steam's marketshare, after Steam helped prove to Epic that the space wasn't as worthless as Epic once claimed, and so Epic has since done everything in their power not to compete on merit or bring in new customers (two options that were well within their power to persue), but to twist the conversation to position themselves as a rhetorical 'good' to Valve's 'bad'. And it's been dishonest as hell, but it's worked on some.
The cut was only ever a strategic concession made in respect to two facts:
1) that EGS is not an especially ambitious platform and thus doesn't demand the R&D/maintenance expense of its competitors
2) that the EGS needed something to claim outward appeal to developers with in lieu of anything else besides publically admitting moneyhat bevahoir that the PC gaming community would have rejected outright
Their emphasis on the cut out of the gate was a calculated PR move whose value lied mostly in putting the onus on 'good behavior' on Steam and in changing the terms of what 'good behavior' meant so that Epic could operate in bad faith under less scrutiny. Epic's core intent is to damage our experience as users of other platforms in an attempt to get us using their own platform, so that we can pay them a cut. And they've realized a means by which to achieve this while positioning themselves shadily as a net-good for the industry, instead of as an entity who is outwardly only in it to take advantage of an ecosystem they see as newly healthy - which is the way Epic and EGS would have been percieved, just like certain superfluous platforms and storefronts before it, if Epic had been honest about the nature in which they actually secured exclusives to their platform.
tl;dr: Epic moneyhats. That's their trick, and you can't directly compete with that without shitting things up for those of us who like PC gaming today. The cut was meant to define and dictate the terms of the conversation surrounding EGS and its competitors, to obfuscate the moneyhatting and to encourage people who otherwise would have resisted the intrusion of EGS to defend it on the basis of altrusim and creating a better environment for developers.
They want us arguing for things that are against our interests as consumers in defense of Epic. And they also want us to collectively pressure Steam into lowering their revenue stream permanently, because from our perspective that's a net good. For Epic, though, it's just another means by which to carve an unearned hole into Steam's slice of the pie and insert themselves fully into it. Valve takes less and Epic is thereby more free to throw around their Fortnite bucks in the manner in which they have ACTUALLY chosen to compete. That's the value of 12% to Epic. Not as an altruistic endeavor, but as a calculated attack against Steam and our experience, that they could then portray as an altrustic endeavor in lieu of literally any other reason for us to consider their entry into the PC space as anything but an intrusion.
