There’s nothing wrong with giving Superman youthful and/or female counterparts except that they’re made redundant by his very own existence. One might say that both Supergirl and Superboy are flawed from the get-go.
Mike Smith pointed out that the problem with Supergirl is that she’s practically redundant. Perhaps even moreso than Batgirl, Spider-Woman and She-Hulk though they’re gimmicks.
She continually gets written out and is made stranger by the minute. Her depiction in the New 52 shouldn’t be that surprising where she became a Red Lantern. On television, she’s Superman in drag.
Funny enough the same can be said of Superboy. He’s a younger Superman, regardless if he’s Kal or Kon. Like Supergirl, he often gets written out which is why all the other Superboys have been getting stranger as it’s already occupied by other characters, including Supergirl herself!
The original Superboy turned out to be a fake or duplicate. Superboy Prime went nuts. Kon’s backstory and personality has been rewritten so often that writers have no idea what to do with him other than get killed and replaced by someone else and then be brought back.
We might have our patience tested with Kon turning out to be James’s brother on Supergirl and realise there’s something wrong with them after all.