Objective observer
Semi-Pro
Firstly you're making the assumption that if Federer was born 5 years later or Nadal 5 years sooner, they'd play the same as he did day for day, despite different matches, different competition growing up and all sorts of variables, which is ridiculous.
Secondly, Nadal didn't play that well in 2017 but had one of the easiest draws in slam history. Federer's level in 2012 was generally better than Nadal's on HC, he's beaten Djokovic in Cincy 6-0 7-6 but had a walkover prior to the berdych match which may have robbed him of some momentum. He also seemed to have a bit of an issue with Berdych at that time
You're also not stating if you're making Nadal 5 years older or Fed 5 years younger. This matters a lot
Yes I am comparing the level from the matches they played