I'm guessing that he never had the pleasure of getting a beat down from Federer. He retired shortly after Federer turned pro.
Becker is 4-10 lifetime against Agassi with the first 3 wins coming before 1990 or before Agassi turned 20. Considering that Becker is only 2 and a half years older than Agassi and their careers had a great deal of overlap that's a rather pathetic record, plus Agassi slacked off during stretches in the 90s. Becker could'nt handle Agassi's return and could'nt consistently hang with him from the baseline. Federer returns pretty well and could outrally Agassi. Federer handles power very well too as evidenced by his consistent success returning Roddick's serve and handling the groundstrokes of power baseliners like Gonzalez. He also has great passing shots on both sides and is a very good volleyer himself. Federer is at or near the top in both holding and breaking serve stats and that probably makes him unique among all past great champions.
Federer does everything equal or better than Becker. The only area Becker is arguably better is maybe the serve but while his serve was considered among the biggest for most of his career more players with big serves started to come out in the 90s so that Becker did'nt even have as much of an advantage anymore even on his biggest weapon. Federer has an underrated serve and was 3rd on the tour in aces last year. Federer has a much better return and return game in general. His forehand is probably the best overall and his backhand one of the best.
In short, I think Federer would win at least 8 out 10 matches against Becker if both were in their prime. It would be closer on grass or fast indoor surfaces but Federer would still have an overall edge. Federer would win almost all of the matches on medium speed hardcourt and absolutely own Becker on clay or slow hardcourt.
The weakest part of Sampras' game was his backhand and his return game overall. Sampras relied so much on his serve and volley game that he did'nt break serve often and had many close sets and matches. While Sampras won most of those matches his backhand and return game cost him a number of matches every year which made it tough for him to keep his losses in the single digits in a year unlike Federer who has done it for 3 straight years and counting. Sampras had at least a few early round exits every year and while he finished number 1 for 6 straight years he temporarily gave up the top spot a number of times during those 6 years because his points advantage was usually slim compared to Federer's stranglehold in the rankings.