I guess it isn't unusual, it's just both players could be the GOAT. Federer already is in many people's eyes but it would be impossible to argue against if he didn't have Nadal around, Nadal could also be the GOAT to most people if Federer hadn't set the bar so high. Not sure if that's the case with most other rivalries, perhaps with some of them. I guess Agassi with let's say 11 slams and a full set might be considered the GOAT if Sampras had never existed
I find this lame for some reason. If you need another person to define if you are the GOAT or not, then you are not the GOAT. Federer is GOAT based soley on all of his achievements.