To say that Agassi would have had "Federeresque" domination if Sampras hadn’t been around is contradicted by the evidence. These are the year-end rankings through the 90s. The only years when Sampras prevented Agassi from being number 1 are 94 and 95.
1990
1 Edberg, Stefan (SWE)
2 Becker, Boris (GER)
3 Lendl, Ivan (TCH)
4 Agassi, Andre (USA)
5 Sampras, Pete (USA)
6 Gomez, Andres (ECU)
7 Muster, Thomas (AUT)
8 Sanchez, Emilio (ESP)
9 Ivanisevic, Goran (YUG)
10 Gilbert, Brad (USA)
1991
1 Edberg, Stefan (SWE)
2 Courier, Jim (USA)
3 Becker, Boris (GER)
4 Stich, Michael (GER)
5 Lendl, Ivan (TCH)
6 Sampras, Pete (USA)
7 Forget, Guy (FRA)
8 Novacek, Karel (TCH)
9 Korda, Petr (TCH)
10 Agassi, Andre (USA)
1992
1 Courier, Jim (USA)
2 Edberg, Stefan (SWE)
3 Sampras, Pete (USA)
4 Ivanisevic, Goran (CRO)
5 Becker, Boris (GER)
6 Chang, Michael (USA)
7 Korda, Petr (TCH)
8 Lendl, Ivan (USA)
9 Agassi, Andre (USA)
10 Krajicek, Richard (NED)
1993
1 Sampras, Pete (USA)
2 Stich, Michael (GER)
3 Courier, Jim (USA)
4 Bruguera, Sergi (ESP)
5 Edberg, Stefan (SWE)
6 Medvedev, Medvedev (UKR)
7 Ivanisevic, Goran (CRO)
8 Chang, Michael (USA)
9 Muster, Thomas (AUT)
10 Pioline, Cédric (FRA)
[…]
24 Agassi, Andre (USA)
1994
1 Sampras, Pete (USA)
2 Agassi, Andre (USA)
3 Becker, Boris (GER)
4 Bruguera, Sergi (ESP)
5 Ivanisevic, Goran (CRO)
6 Chang, Michael (USA)
7 Edberg, Stefan (SWE)
8 Berasategui, Alberto (ESP)
9 Stich, Michael (GER)
10 Martin, Todd (USA)
1995
1 SAMPRAS, PETE
2 AGASSI, ANDRE\
3 MUSTER, THOMAS
4 BECKER, BORIS
5 CHANG, MICHAEL
6 KAFELNIKOV, YEVGENY
7 ENQVIST, THOMAS
8 COURIER, JIM
9 FERREIRA, WAYNE
10 IVANISEVIC, GORAN
1996
1 SAMPRAS, PETE
2 CHANG, MICHAEL
3 KAFELNIKOV, YEVGENY
4 IVANISEVIC, GORAN
5 MUSTER, THOMAS
6 BECKER, BORIS
7 KRAJICEK, RICHARD
8 AGASSI, ANDRE
9 ENQVIST, THOMAS
10 FERREIRA, WAYNE
1997
1SAMPRAS, PETE
2RAFTER, PATRICK
3CHANG, MICHAEL
4BJORKMAN, JONAS
5KAFELNIKOV, YEVGENY
6RUSEDSKI, GREG
7MOYA, CARLOS
8BRUGUERA, SERGI
9MUSTER, THOMAS
10RIOS, MARCELO
[…]
122 AGASSI, ANDRE
1998
1 Sampras, Pete
2 Rios, Marcelo
3 Corretja, Alex
4 Rafter, Patrick
5 Moya, Carlos
6 Agassi, Andre
7 Henman, Tim
8 Kucera, Karol
9 Rusedski, Greg
10 Krajicek, Richard
1999
1 Agassi, Andre
2 Kafelnikov, Yevgeny
3 Sampras, Pete
4 Enqvist, Thomas
5 Kuerten, Gustavo
6 Kiefer, Nicolas
7 Martin, Todd
8 Lapentti, Nicolas
9 Rios, Marcelo
10 Krajicek, Richard
2000
1 Kuerten, Gustavo
2 Safin, Marat
3 Sampras, Pete
4 Norman, Magnus
5 Kafelnikov, Yevgeny
6 Agassi, Andre
7 Hewitt, Lleyton
8 Corretja, Alex
9 Enqvist, Thomas
10 Henman, Tim