I don't have much to add except to say that I'd be hesitant to use head-to-heads as a deciding factor in determining who is the best or better player all-time.
Matchups play a huge role in the resulting head-to-head records between different players. History has shown that great players sometimes have poor records against inferior players simply due to a style match-up - using this as as a determining factor can lead one astray.
I also want to agree with the notion that the Hamburg '93 Seles stabbing altered the course of women's tennis that it is difficult to know exactly how the major totals would have been different if that never happened. It's interesting to speculate about though.