It's not a surprise because anyone can see Roger can adapt to any playing condition. As successful as he is on slow courts in the past years, he would even be better with a faster courts. So given Federer playing in an era of serve and volley, he would have a field day.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi