Where did you get that from? I’d be really surprised if it were true… I’m a real rooky in both UE4 and c++, but even at my stage I can see the superiority of c++ in almost every aspect, be it processing speed, clarity of logic, portability (with c++ you can literally copy/paste, not only a class, but a whole system project to project with very little hassle, try doing so with BP)…
Blueprints are superior for faster iteration and accessibility for designers. That would lead me, if I had to guess that Fortnite would be more 80% c++ and 20% BP 