Here’s the thing about non-canon ships. They are ships that are chosen by fans of the show by what they see on screen, these ships will almost all of the time never be canon, because of the logistics of the show. Any fan is free to ship any pair of characters they want if it makes them happy.
But please remember that the ideas you have yourself about the characters and the ideas the writers have will be different. This is why fanfiction exists, so you can creat your own worlds and scenarios for the characters.
Jeremy saying Kara and Lena will never get together is not him being disrespectful. It’s him being honest and not leading anyone on with queer baiting. The cast know that Supercorp is widely shipped and don’t want anyone getting their hopes up.
“If Lena was a man” yes, IF, but she’s not, and with Kara in the show being a straight character, she will be only friends with Lena. As much as I ship Supercorp I ship it AU, as in in fics, but in the show i’m cool with them being just friends.
And here’s why i like Kara and Lena being just friends. Kara, since Lucy leaving the show, doesn’t have any female friends that we know of, she has her sister yes, but that is different to having a friend away from the family, and she has Winn and James, but them being boys she won’t bond with them like she would a girl. And where she is getting to know Maggie more, she is still her sisters girlfriend first. So personally i think it’s really important to give Lena a female friend to talk to, confide in, and protect. They have a strong friendship based on belief in each other.
I know how important it is to show LGBT representation, but you can not decide a character is gay when they are not. What you make of a character in your own fanfictions or fan art is each to their own. But remember to separate AU from the written show.