The marketplace not having ROI and at least break-even CAN be true. I guess the marketplace stuff is developed by external devs, and thats usually not cheap. Adding in that maybe Epic uses SAP, costs already explode.
Additionally doing everything in the marketplace by hand of course leads to much costs vs automation. And then we have the fun thing that its barely even and the boss doesnt want to invest more money for now, which results in even higher costs since the marketplace volume gets bigger and more stuff must be done by hand.
IF that statement was not true and the marketplace is actually successful, now that would be a punch in the face when the boss of the company we (more or less) love blatantly lied to the sellers that actually help that company to get more money through the marketplace AND attract more indie devs through this.
Though, we will most likely never find out.
And of course, talking about other companies that they should reduce their cut is much easier than reducing your own cut, regardless of having break-even or not, since suddenly its your money and not of the others.