Let's look at 1990-1995 at the non-French Open Majors. If we transport Murray back to those tournaments, he might need to beat:
AO 1990: Lendl, Edberg, and Wilander/Becker
AO 1991: Becker, Lendl, and Edberg
AO 1992: Courier, Edberg, and Lendl/Krajicek
AO 1993: Courier, Edberg, and Sampras/Stich
AO 1994: Sampras, Martin, and Edberg/Courier
AO 1995: Agassi, Sampras, and Chang/Courier
WI 1990: Becker, Edberg, and Ivanisevic/Lendl
WI 1991: Stich, Becker, and Edberg
WI 1992: Agassi, Ivanisevic, and Sampras/McEnroe
WI 1993: Sampras, Courier, and Edberg/Becker
WI 1994: Sampras, Ivanisevic, and Becker/Martin
WI 1995: Sampras, Becker, and Ivanisevic/Agassi
UO 1990: Sampras, Agassi, and Becker/McEnroe
UO 1991: Edberg, Courier, and Lendl
UO 1992: Edberg, Sampras, and Courier/Chang
UO 1993: Sampras, Pioline, and Masur/Volkov
UO 1994: Agassi, Stich, and Martin
UO 1995: Sampras, Agassi, and Becker/Courier
Those are brutal draws other than the 1993 U.S. Open, where Murray would still need to beat peak Sampras in the finals. If Murray were born in, say, 1970, it's tough to see him winning more than 2-4 Majors, which is no knock on him. He's right there w/Courier below Edberg/Becker/Wilander.