Basically, everything that isn't about Kara, anything that pulls focus off her, is not great. And the biggest thing pulling focus off her in this show is Superman. And the way they treat him exacerbates the situation, because they're literally treating him as such a superior being that they won't even speak his fucking name.
For a large part of the show, Kara's motivation is realizing her potential, and helping people, making a difference, and starting to feel like she actually does belong in her own skin. That shit is charming as hell the way Benoist plays it, and I invest in that pretty strongly when that's happening. But then they undercut it by essentially adding a heavy glaze of "If only I was as cool/strong as my cousin! I hope he approves of me!"
Not that there isn't a way to do that (look at Spidey and Captain America in the comics, for example) but you either need that superhero to be around every now and again, and one-on-one interacting with our protagonist, or you need that hero to die so OUR hero can step up.
In fact, for a quick second there, I thought this was essentially going to be a riff on Spider-Man, starring Supergirl, and I thought that was a decent way to go at it.
And yeah, as Cheebs pointed out, the level of threat this show introduces makes it really weird that the Superman won't show up. That's not the kind of shit Superman would shrug at and go "eh. Cuz has that one."