Hingis being greater than Henin is no slam dunk. Only if you only look at 7 slams vs 5, but if that was all that mattered Margaret Court would be the GOAT. Hingis has all those weeks at #1, most before the ridiculous ranking system began. She has a great doubles career where Henin has achieved squat all in doubles. Lets say you even gave doubles slams 10% the value of singles it would still bring the two very close already. Hingis was far more precocious, becoming youngest ever slam winner, youngest ever #1, these are things she will be in the history books for a very long time, who knows maybe forever. What will Henin be remembered for, her Roland Garros record, it is nice but there are a number of better records at the event in history even there- Evert, Graf, Lenglen, Court. Her great 2007 year, again nice, but there are probably a dozen better years in the Open era including Serena's 2002 and Hingis' 1997. Had she won Wimbledon she could have really made that a special year that ranks alot higher up, including probably above those two I mentioned, but too bad Bartoli had other plans.
One thing is for sure, regardless who is greater, Hingis made more impact on the sport. People still today talk about Hingis as possibly being the smartest, most creative, and most tactically astute player in tennis history. Henin is basically a combination of a wannabee poor womens big babe after lots of weight and strength training (the extra power her only edge over Hingis really) and a poor womens Hingis kind of mixed together into one player, so obviously alot more effective than if she were only one of those things, but not really an extra special type of player in anyway other than maybe the hardest hitting 5"6 player ever as if anyone really cares about that, lol! An overachiever who was never marked for legends status coming up, but found her niche vulturing a weak clay era, and capatilizing on the injuries and declines of various stars in the mid 2000s. Good for her though, she certainly took ALL her opportunities and made the most of her comparatively limited talents, and she deserves her status as the best clay court player of her era, and fully deserves all her 7 slam titles she won and status as a 7 slam singles winner, but is it clear cut she is overall superior to Hingis and Venus as her fans make it out to be, definitely not. Especialy when those two had far more impact on the sport and excelled in both singles and doubles in a huge way (and Venus even has the same # of singles slams to boot). Hingis also excelled in the all time golden age of the womens game from 1998-2003, the same one Serena stamped her greatness so emphatically by dominating such a deep field late 2001-mid 2003. Henin vultured in the absence of the Williams and capatilized on the start of the dry spell for the WTA, admitedly nowhere near as bad as today yet, but nothing like the era the Wiliams and Hingis won many of their titles in. When people talk about the glory period of womens tennis that was a period that people will recall included Serena, Venus, Hingis, Davenport, Capriati, Graf in her later years. Henin had a little era of her own but it will be remembered as the post Golden period basically once all of those went down or retired.