I think the big difference, to me, is the expected fandom response to it. I mean, we all are in fandom here, and I presume a lot of us make fanfic or fanart, or at least talk about what we'd like to see happen to the characters.
If you say, 'I don't like character X, she's a vapid romantic stereotype,' I'd expect you to marginalize character X, putting her aside in favor of the characters you like more. Depending on the circumstances, that might entail killing them off or otherwise causing bad things to them in your fanwork, or it might just entail ignoring them entirely.
If you say, 'I don't like what the writers have done with character X, they're treating her like a vapid romantic stereotype,' that implies there could be something salvageable about her. From someone taking this tack, I'd expect to see fanwork that might attempt to redeem her. The damsel in distress gets her own adventures and gets to save herself. The background love interest is seen at her own job, which it turns out is a dramatic one she's surprisingly good at. The faux action girl gets to actually save the day and show off her skills without getting taken hostage by the villain. Even if she doesn't end up the focus of your stories, she might show up in a supporting role without the flaws she's subjected to by her canon treatment.
Fandom is very frequently transformative. People often feel they can do better than the writers, and sometimes they're right. Not blaming the characters for the failings of the author is one of the key steps in transforming them sometimes.
Re: OP
If you say, 'I don't like character X, she's a vapid romantic stereotype,' I'd expect you to marginalize character X, putting her aside in favor of the characters you like more. Depending on the circumstances, that might entail killing them off or otherwise causing bad things to them in your fanwork, or it might just entail ignoring them entirely.
If you say, 'I don't like what the writers have done with character X, they're treating her like a vapid romantic stereotype,' that implies there could be something salvageable about her. From someone taking this tack, I'd expect to see fanwork that might attempt to redeem her. The damsel in distress gets her own adventures and gets to save herself. The background love interest is seen at her own job, which it turns out is a dramatic one she's surprisingly good at. The faux action girl gets to actually save the day and show off her skills without getting taken hostage by the villain. Even if she doesn't end up the focus of your stories, she might show up in a supporting role without the flaws she's subjected to by her canon treatment.
Fandom is very frequently transformative. People often feel they can do better than the writers, and sometimes they're right. Not blaming the characters for the failings of the author is one of the key steps in transforming them sometimes.