Superstar gives you a bigger bonus, by far, than anything else. The only bonus (if I remember right) that a different trait has that superstar doesn't do is Easy Going's chemistry bonus. Literally everything else a trait has, Superstar has and does better. Getting a 4th trait would be piling on.
With the level of RNG in the sim compared to the price of SS both in real cost and cap space I dont think it'd be overpowering at all. Basically every other trait has a corresponding downside.
But I don't think it would happen either. Not enough benefit I guess.