Lol, you don't remember any shows where Clark "stole" Kara's villains because SHE'S the legacy character. She was a part of his world from the moment she was created. Her villains are his. And yes, on a show centered around her, if she gets to encounter a few of the smaller-time ones first herself, that's well within their rights and not remotely "disrespectful" of the writers to do. They established the most iconic ones to be his first (and for the record on the ones you mentioned, Henshaw even on this show was Superman's villain first, just not in his Cyborg form, and Toyman was also put in prison first by Supes), and established him as the great hero of Earth with statues and parks named for him, whose universally beloved by the public, with many famous victories under his belt, whose shadow Supergirl had to get out of. Superman's had multiple versions and encounters with those smaller time ones on his own shows/media, so it's hardly an injury to him for her to get a few them first on her show.