It wouldn't matter how you try to explain Linda's time as Supergirl or when you set it Kara within the wider sphere of pop culture is and always will be Supergirl and that's not going to change the same way Barbara Gordon is Batgirl despite Bette Kane existing several years before her also are you seriously trying to compare Kara's being stuck in suspended animation on her way to Earth (a common sci-fi trope present in many movies, tv shows..etc) to Linda whole Matrix/Earth Angel debacle because that some false equivalence.
It's not matter of audience intelligence it's just cleaning up messy storytelling because superhero comics have a tendency to mistake complexity for depth.