Some women are insufferable cunts, it portrays them accurately haha %)
Also - the sister is definitely a twat, but Skylar? Not the kinda personality I'm into, but I'd hardly say she's a cunt. Yeah she was pretty cold last season, but she's also coming off realizing that her husband and her whole life is completely full of shit. The entire series only takes place over the course of a few months to this point, AFAIK. When we saw her in Season 3, she was only a few weeks into knowing the truth about Walter.
Alsox2 - Marie (the sister) who is a certifiable twat no doubt, was significantly humanized after Hank was shot and I thought the actress that plays her did a GREAT job playing a much different role from the one she had spent 2+ seasons building up in those episodes.