Maybe it doesn't matter as much what system you use so long as you have a system. In one of my favorite movies, Project A-ko, the main characters are based upon the personality traits of the different blood types. Yeah, in Japan there is an old belief that blood type determines personality which makes no more or less sense to me than personality based upon astrological signs.
In Alien Fiction, I use the signs of the Chinese Zodiac as my starting point. The rabbit sign is supposed to be sentimental and fun to be around, My rabbit character is a greatly exaggerated version of these traits.
She is also a mirror of my own extrovert side. The system didn't need to strictly define the character, just provide a starting point. The reason we use a system is so the characters come off as being diverse and not the same character in different skins.