From 1968-1974, Rosewall skipped AO 2 times, RG 5 times, Wimbledon 2 times and USO 1 time.
From 1969-1976, Newcombe skipped AO 0 times, RG 5 times, Wimbledon 3 times and USO 2 times.
From 1974-1981, Borg skipped AO 7 times, RG 1 time, Wimbledon 0 times, and USO 0 times.
From 1974-1989, Connors skipped AO 13 times, RG 7 times, Wimbledon 0 times, and USO 0 times.
From 1977-1992, McEnroe skipped AO 10 times, RG 6 times, Wimbledon 2 times, and USO 0 times.
From 1980-1991, Lendl skipped AO 2 times, RG 2 times, Wimbledon 1 time and USO 0 times.
From 1985-1996, Becker skipped AO 2 times, RG 3 times, Wimbledon 0 times, and USO 1 time.
So from these 7 ATGs, AO was skipped 36 times, RG 29 times, Wimbledon 8 times, and USO 4 times. So historically, it should be clear where the Slams stood in how prestigious they were. Now today, I would say Wimbledon is still the cream of the crop because of its history but all the others are about equal. RG is lagging behind the other 3 though and needs to catch up.