Umm you obviously did not watch some of their matches. Graf has flat out overpowered Seles.
http://www.youtube.com/watch?v=pwdeBBzhdPA
http://www.youtube.com/watch?v=YiFHwjWBNnI&feature=relmfu
http://www.youtube.com/watch?v=WKUCsHTMXWI
Also Seles pre stabbing had quite good mobility, not Graf or Sanchez level, but as good as pretty much anyone else on tour at the time. Seles ONLY had problems with people who had as much or more power than her, people like Davenport, Venus, Serena, Graf, and on occasion Pierce and Capriati. All except for Hingis, who was a tactical genius with impeccable timing, the best ball control in the game at the time, and who negated her power deficit by being the only player at the time who took the ball as early as Seles did. You did not beat Seles by just maneuvering her around, those who tried to do that got the crap beat out of them regularly- Sabatini, Sanchez, Huber, Majoli, Martinez.
Graf has a bigger serve than Seles, a bigger forehand, move penetrating volleys, and a bigger overhead, so how can Seles be WAY ahead in power. I would rate them roughly equal in power, whoever is ahead is only 1 or 2 people ahead of the other at best. Either way there is no way people like Azarenka, Ivanovic, Capriati, Dementieva, even Clijsters overall rate above Graf in power. The only players who have more power than Graf are ones who hit very hard off both sides and some cases have bigger serves. Those players (minus Azarenka who has a better backhand than forehand, better return than serve, but unexceptional power off any shot) are pretty much forehand only players like Graf, and Graf easily has a bigger forehand and bigger serve than all of those. What shot does Ivanovic hit with more power than Graf, lol!