Sampras' such long reign is completely worthless. His 1998 ranking/performances were comparable to Del Potro's in 2009 - and while Sampras finished the year 1st Del Potro was 5th LOL.
He was the flat out best player in 1993, 1994 and 1997. In 1995 Agassi was better but he injured himself at the end of the year and Sampras just barely continued his reign (the difference was like 100 ranking points despite Agassi missing the last 3 months of the season). In 1996 Sampras won only 1 major, lost in one quarter and one semi, won no Masters yet he still comfortably ended the year ranked 1st. It says how weak the tour was.
Federer lost like 20 matches in 2004-2007, his reign was an actual reign, not just being "barely" better than anyone else from his generation like Sampras did. Heck, guys like Moya, Rios, Muster, Rafter could take away the top spot from Sampras while Federer lost his top ranking in August 2008 to a GOATing Nadal.
Just shows you how pointless H2H's are. Nadal beat Fed but in the end it meant jack, they both walked away with nothing. It's about winning titles.