Uhh, 10 years ago, Martina *WAS* beating Fernandez & Zvereva. (Zurich 1993). Her matches against them were always close.
Martina was ranked #5 in doubles when she retired from singles. However, during those last years, she also had singles to deal with and she did not play doubles at all events. Had she only played doubles back in 1993 or 1994, I'm confident she would have won a Slam or two.