If we see another random one-time winner, the RG will continue to lose credibility.
You cannot say like this, even they are only one RG winner, they are still the top players and some of the best players in the tour.
2000 Mary pierce won 1995 AO, and F in 2005 FO, 2005 USO
2001 Jennifer Capriati won AO 2001 2002, reached SF in Wim and USO
2008 Ana Ivanovic also got F in RG 2007, AO 2008
2009 Svetlana Kuznetsova won 2004 USO, reached QF in AO and Wim
2011 Li Na, reached F in AO 2011, 2013
2012 Maria Sharapova, Won Wim 2004, USO 2006, AO 2008
Maybe Myskina and Schiavone are a little random but they both still reached QF in other three slams.
Saying them random actually is not appropriate as many players cannot even win a slam or cannot win RG.