[1] https://cdn2.unrealengine.com/apple-complaint-734589783.pdf
[1] https://cdn2.unrealengine.com/apple-complaint-734589783.pdf
The word you’re looking for by the way is “financially”. Fiscally is to do with taxes.
The OED establishes a North American usage of this term as "relating to financial matters", and is not exclusive to taxes.
It seem like something their lawyers pitched to them as “hey if it works, great, you save millions a year on the App Store percentage, and if it doesn’t, hey, at least you’ll get a whole lot of publicity, which should drive your sales up enough to more than compensate for the losses of being off the stores for a bit.”
Epic is the maker of unreal engine, which collects a 5% royalty on licensee game sales over $1M.
So they would stand to profit somewhat more than just from lower fees on Fortnite.