What matters more to the verbal aggression is how Luigi reacts to it. I still remember Starlow seriously talking down on Luigi when Luigi's asleep and sleep-talking (asking?) her to touch his face because he can't communicate any other way to help Mario, as Mario does ask for Luigi's help. Starlow, conveniently forgetting WHY Luigi is sleeping, as Mario is inside his head, just responds with "First the stache, now the nose?! What're you, five years old?!", similar nastiness. Luigi can't react to that given that he's asleep, but Starlow is being unnecessarily abrasive and isn't concerned for EITHER brother.
I *think* they're trying to play it for a joke (remember the Star Gate from Mario & Luigi: Partners in Time mocking Luigi as a joke that lead to Luigi crying, but the Gate was proven wrong and apologized and even called them the "best siblings ever"), but how Luigi is developed as a character, a vulnerable self-conscious type, he doesn't come off to me as a the type who'd shrug off insults. This is on top of the situation going too far with the joke, so there's a kind of unsettling feeling you get if you empathize with Luigi and you read Starlow's words. If Starlow was like that toward Mario, Mario CAN react with just an angry face and/or ignoring her. I don't know how often Luigi reacts to it, if he does at all (but even if he's oblivious, it doesn't excuse Starlow). But what you're describing above is unnecessarily cruel. This is mean-spirited emotional manipulation and I think the words are too uncomfortable to sit through. According to her article, she did apologize at some point, probably wasn't enough though.
I don't understand AlphaDream's fixation on treating Luigi crying as a joke either. When a person like Luigi cries over the Star Gate or Starlow, you're not supposed to laugh.
And I don't know if Mario ever comes to Luigi's defense. My memory's not good enough. But if he doesn't, I assume obliviousness on his part. It just doesn't seem right to depict him as a person who intentionally stands by while Starlow berates Luigi. At the Star Gate part, Mario does object. When Starlow mocked Luigi's crying from Partners in Time and said "Mario probably killed the Shroobs anyway", upsetting Luigi, Mario said, "Yeah, that's not true, Luigi did save the day (don't you downplay Luigi like that)." which leads her to apologize. Also according to the article, she's more respectful to Luigi in Paper Jam, but from the above convo, doesn't seem like it?
In Paper Jam, Starlow also thinks she's the leader of the group. Hell no.
Oh, and Starlow replaced Toadsworth for tutorial-giving. Wonderful.