Importance order of grand slam tournaments

The French Open has had more one hit wonders (people who won no other majors) or people who only won that major than any of the other grand slam tournaments in the open era. However you could argue that that is down to it being on a different surface to the other grand slam tournaments. OHW include Gaudio, Moya and Noah, people who only won the French Open include Kuerten and Brugera.

The Australian Open has also had one hit wonders like Thomas Johansson, Djokovic and Korda. You could argue this down to different factors. One it is at the start of the season and takes some players by surprise. Two it used to not be viewed as on the same level of importance as for example Wimbledon. For example Borg didn't use to play it.

However Wimbledon and the US Open seem to have the most number of winners who also won at least one other different grand slam tournament. Winners of both include Sampras, McEnroe, Becker, Federer and Agassi.

The following data is for the Open Era. Source = en.wikipedia.org/wiki/List_o...

8 players have only won the Australian Open, who also only won it once. This includes Tanner and Johansson.

11 players have only won the French Open, 9 of which only won it once. This includes Bruguera and Costa.

4 players have only won Wimbledon, all of which won it once, including Krajicek and Stich.

3 players who won US Open didn't or haven't won any other Grand Slams. They all won it once and they are Andy Roddick, Juan Martin del Potro and Manuel Orantes.

EDIT: Kafelnikov won the US Open