So if the Masters counts a major in the 1974 and 1975 which I agree does make sense as it was a very big tournament, does that mean the significantly less important Australian Open, where Vilas won his 1978 and 1979 titles when hardly anyone cared about the tournament before 1983, wasn't a proper major?
Vilas never beat Borg in a best of 5 set match apart from the 1973 Buenos Aires final. Borg was only 17 years old and leading by 2 sets to 1 in Vilas's home city, before colliding with the umpire's chair at 6-6 in the 4th set and having to retire injured.
After that Borg won every best of 5 set match they played, Rome in 1974, RG, Boston and Barcelona in 1975, Dallas and Wimbledon in 1976, Nice in 1977, RG in 1978 and Monte-Carlo in 1980. A lot of those matches weren't even close with Vilas getting crushed.
Vilas had more chance of winning the lottery than beating a Borg at RG in 1980 or beating a prime Borg in a best 5 set match anywhere on any surface.