It would be perfectly fine with Apple for Epic to sell Vbucks on their own web site, or through other platforms (which they do), and Apple would not ask for, no

It would be perfectly fine with Apple for Epic to sell Vbucks on their own web site, or through other platforms (which they do), and Apple would not ask for, nor would it have a right to, a cut of the fees. What you can not do in an iOS app is direct someone to another payment processing platform to purchase digital goods to be consumed within the app. Customers have to figure it out on their own.