This is the reason I kinda dislike the poll and when people refer to it; it's soooo easy to draw bad conclusions from it.Thats the thing when you have 7 LIs. This is basically the number which is still ok, but if it turns into more, it just leads to some LIs not getting enough action. Especially when they are unpopular (which is the case for Penny, at least according to the votes on the screenshot which was going around a few days ago).
And IMO, Penny is currently the weakest. She does not have much what makes her stand-out compared to others, other than being pretty with big boobs. But again, she did not have much content lately, so no wonder she comes off a bit bland.
The truth is that Caribdis has created 7 LI's who are all liked by nearly everyone, which is a rare feat in this business. I would bet that if you made a poll on any of the LI's with the simple question "Do you like character X, yes or no?", or alternatively "Are you happy with the inclusion of character X in the story, yes or no?", every girl would have 85%+ answers yes. Claiming that any of the LI's is unpopular is wild.