My issue with the Alex/Maggie B-plot is that it was out-of-place within the context of the episode. Full Stop.
However, that's not really the point here. You don't have to like the way that Alex and Maggie fit into this episode, but to sit here and claim that original characters are somehow "less" because they're original is to peddle "Alternative Facts" and lessens your credibility.
Actually unless that character takes off, and sorry, Alex isn't some sensational character that came into her own, it does matter that the character is brand new. The show wasn't sold as Alex's story. People don't watch superhero shows to see the adopted sister of the hero.
She is a supporting character. That's great. But to devote as much time, especially out of context, isn't working at all for me.
This is just something I feel the writers are forcing because they like it, regardless if it is working or not. Their choice, but I don't have to pretend to like it when it takes away from the real story, which it absolutely did this week.