What's your problem dude, can you actually realize the FXX does NOT produce the same downforce of a Zonda R nor a GT1 race car because wasn't Ferrari goal doing that? FXX is a TUNED car used for research and develop programm.
They already have done a race car out of Ferrari Enzo, it's called Maserati MC12 GT1.
That car feature the same engine and chassis of the Enzo. While being equiped with a different bodyshape and being limited by FIA rules (smaller rear wing compared to opponents and smaller front splitter) still managed to win GT1 championship 5 times in a row.
I don't have a problem.
The FXX is a fantastic race car.