3. Kara Danvers and James Olsen
It's interesting watching Supergirl's first season back because everything feels so larger-than-life; so cinematic and new. It's definitely aged well, and it's a constant reminder of what the show could have been if it stayed on CBS (a.k.a. we could have had five more seasons with Calista Flockhart).
One aspect that doesn't hold up is the romantic plot between Kara Danvers and James Olsen. The pair didn't have that much chemistry and it was kind of pointless watching them fall for each other when the creatives confirmed that they couldn't end up together. Moreover, James could be quite arrogant whenever the plot dictated him to be, and that wasn't charming in any way (remember how intolerably jealous he was when Barry Allen showed up?).
There could have been potential here, but the whole "opposites attract" trope didn't offer much beyond surface level will they/won't they, and fans just struggled with it as a result of that.
While the Girl of Steel deserves happiness, this romance felt very by-the-numbers and it actively took away from the show's main storyline. The fact that there was such a hard pivot in the season 2 premiere says all you need to know about how successful this one was.