I think, in my opinion and personal experience with Libras that their indecisiveness comes from what they actually symbolize, a scale; they're an air sign= communicators, thinkers, logical minds so while they're the judges of the zodiac (along with some other signs) they're also diplomats and people pleasers, they want an harmonious and rewarding life after all; so I think that, in order to do this in this way they need to put on the plates, on each side of the scale everything they need to consider, in order to make THE best decision. So I think it could also be reasonable for them to "make a mistake", because absolute truth , perfect choices simply don't exist, and maybe because they get anxiety and so on from doing that, as they don't like to be constantly in the spotlight (mars fall); while I think that virgos, for example, are that kind of judges (as you were saying, more in an analytical, meticulous way) they are more, not blunt, like they always care in what they believe, and most of the time they have reasonable motives to do that, not that they're better in this way but they're simply less people pleasers and more of "I speak for myself" kind of ppl. For those reasons I think that Libras are the less cardinal sign in this way, their still cardinal (active, ambitious people) but they could have troubles with being initiatiors and decision makers, I'm afraid.