I kind of agree on statement, that most anime characters differ solely by haircut. Of course, this relates only for characters inside a certain style.
I've discovered, that it's very hard, to maintain uniformity and homogeneity when dealing multiple characters. You may want to make them different, but at some point they start to look inappropriate and fall apart. So you have to stick to some rules and key features allowing only limited variation at some places.
So this was an experiment to make a character look different by changing only hairstyle.