A lot of other possibilities, Connors in 1974 won three out of three majors entered. He couldn't enter the French Open because players who played WTT weren't allowed to enter. He was either 99-4 or 93-4 for the year.
McEnroe in 1984 won Wimbledon and the US Open with an 82-3 won-lost record. He won 13 tournaments out of 15 entered. He destroyed people, not just beat them that year.
A few of Borg's seasons in the late 1970's deserve great consideration.
It's a long time ago
but Djokovic's 2011 season deserves great consideration also. Any old timers remember 2011? lol.
Maybe the best season of the Open Era was Steffi Graf's 1988 season with the Golden Slam. And of course many of Martina Navratilova's seasons from 1982 to 1986. Margaret Court won the Grand Slam in 1970 and many of Chris Evert's season are up there also.