No no no, the 12% was not on the charges from all the payment methods. Epic was saying it was up to 25% on every transaction purchase made if they continue to add even more options. The 12% mentioned was a cut is a store cut. Meaning, they take only 12% revenue from its clients. This 12% cut makes them super competitive against others because they net about 5% and have (had) a chance to grow it to 6-7%. Leaving the rest (88%) for those who created the games.
Xsolla may only charge 5%, but others charge far, far more. As Epic learned. 