True, playing second fiddle to Superman would really annoy Lex no end. But Jimmy had multiple superhero identities (admittedly mostly sidekicks) and his own title, back in the day. He's not exactly the tea boy anymore.
I'm not saying it a bad story point, because it does work. I'm just saying it could've been more creatively. Like, say, Lex running a street stall selling Superman tshirts.