I disagree. Either way it would be close and not the slam-dunk you make it out to be. If Henin, Raadwanska can deal with Williams' power enough to give her close matches to say that a peak Graf couldn't is looney. Not to mention that I'm not sure Williams is the hardest hitter on tour.
BTW #1 is always "on paper."
I know Henin was a tough opponent for Serena, but maybe Henin in her prime is better than Graf. I know some will laugh at that, but Henin played in a way tougher era and her career was basically over at 25 so I dont think stats alone tell who is better at their best. Anyway all of Henin's success vs Serena is based on either:
-clay court matches, and I concede Graf is better than Serena on clay, and Henin might be even better than Graf on clay anyway, some consider her the #2 or #1 clay courter of all time after all.
-Their 2007 matches, and I would say Henin in 2007 was at a higher level than Graf ever was in sheer playing level, regardless of stats. Apart from grass of course but a healthy and in form Serena, even not at her best, would always crush Henin on grass anyway.
-The 2004-2006 period when Serena was at her worst ever anyway.
Comparing Henin to Graf Henin has a way better backhand, much better return of serve, is better at the net, has more variety, moved nearly as well and overall played better defense. Graf had a much better serve and forehand of course.
As for Radwanska she is no competition for Serena, fluke 1 set won in the Wimbledon final aside. Anyway that is Serena at 31, what were Graf and Seles doing at 30? Yeah they were retired.