Past prime Federer is doing better than a pre-prime Federer. During his early year, he was consistently losing to Hewitt, Nalbandian, Henman, Agassi, etc. I know he beat 4 times defending Sampras at Wimbledon in 01 but he wasn't a slam materials yet, and not in the top 5, let alone reaching #1. However, past prime Fed today who is facing Nadal/Nole/Murray is doing much better than teenage Fed.
When you think about it, Hewitt/Safin/Agassi/Nalbandian and company get slighted when comparing to the top players today.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi