Don't go down that path....Fed had a back injury and didn't even practice on the USTA grounds in 2017. He could barely move in the Canadian final against Zverev.
A healthy Fed would have been prohibitively favored in a 2017 USO final against Nadal. He beat him like a drum all year, including 7 weeks after the USO in Shanghai. Anyone saying it would be "unlikely" that Federer wouldn't have beaten Nadal in 2017 wasn't watching tennis in 2017.