It also helps, as Kreisberg notes, to bridge the gap between the mythos of the two characters that’s been built up in the comics.
I think it was a wise choice for the Supergirl team to lean into the idea that Clark has a bigger impact on people than Kara does.
By having the show recognize the differences in popularity between Superman and Supergirl, they’re letting our own expectations of the characters feed the storyline, which just seems like a brilliant idea.
It is a good way to use the natural contrast between the two characters, where Kara is still a newcomer to fighting crime, and is best known at home, and Clark has been helping people all over the world for several years by now.