I could not agree with your first statement more.  Brendan Frasier is not a bad actor at all.  He's just an actor who wants to make money more than he wants to make art, and thus will scribble his name on anything that gives him a reasonable paycheck for someone in his 'fame range,' as it were.

I completely disagree with this for the simple reason that Jackie did
nothing that Veronica herself wouldn't do if she felt like she was in
the exact same situation and felt wronged by someone who was muscling in
on her territory.

For me, I think that it actually works because of the very nature of what it is.  Cox doesn't love Carla, but he thinks that he loves Carla because he's a fucked up individual who has problems understanding the idea of love, and Carla is one of the warmest and most emotional relationships in his life.

If you're a fan of nods toward continuity that reward the audience for sticking around, you're going to love some Scrubs.  There are a few continuity errors here and there, but there's a lot of continuity where seemingly throwaway jokes end up coming back, and even sometimes as full blown characters.