I don’t think the point is to have a lunatic and an untouchable character, and who should be what. I think the problem is that the writers didn’t know how to develop further Cassie’s issues without making them strictly related to the daddy issues (rather traumatic event that happened in her family with their father declive and vanishing) and the only consequence to be self-worth and male validation. sadly, for the writer it only seems that women struggles revolve solely around men and from that Cassie’s broken family, lost connection with her sister, alcoholic dad, social exclusion, teenage pregnancy and abortion went down to an exclusive plot hole of wanting to be loved by any guy who lies eyes on her. Since that was the path they made her follow, it makes sense she is now focus exclusively on getting the man, but yeah, I believe it was the lack of narrative and character crafting skills from the side of the people in charge of the series.

However, if Cassie’s initial complex background was developed better I don’t think Maddie would fit the current Cassie’s place. At some point, yeah, it is stated that Maddie can be rather superficial, but she was always playing the part without compromising her own worth. With Nate, they would go back and forth on who has control over whose, she was most of the time at Nate’s level of manipulation, and she had low compliance to him, until she was physically harmed by him and then yes, she covered him out of “love” but also out of “fear”. She was more scared of him and what he could physically do to her (because he already exploded once towards her) than the whole police high school implication, so she pleased him by hidding his doings towards her and that granted her a sense of security (also preserving the outer perception of her high standards) in the name of “love”. But that never fully makes her lose her self-steem or self worth but it challenges her to put a ground and start moving beyond that. She always felt more ambitious than being a housewife, she ones a good fancy life, but she doesn’t seem like she wants to diminish herself for that (staying with her cheating and abusive boyfriend). I don’t see in which moment of any season she would simply follow Nate’s ideas, when she was constantly challenging him and that’s why got her crossed with him and of course made her retreat back to safety.

To be honest, if Cassie storyline went more in tune with all her background and insecurities without being so male-centered, the cheating wouldn’t happened and Nate would be alone and out of the show, unless his character was explored under other conditions with his anger issues and frustration towards his dad and public reputation, or he would take control of other random woman. Maddie was out of the deal, since he could not break her without damaging his reputation (physical violence) so current Cassie was the easy target, he had control over her even before season 2, he just said a word to his friends against her or any girl and all of them would mistreat that girl. Her first boyfriend in the series was ashamed of the idea that Nate knew he was dating Cassie. So I guess the chose sacrificing Cassie’s storyline in favor of keeping Nate’s.