I think Leslie would have been a great addition to the show and would have loved seeing her. In my alternate universe where she exists, alongside her helmsman role, I made her Picard's yeoman (which despite the female TOS origin connotation for that, I based their relationship on Bartlet and Charlie from "The West Wing")
That said, I think God that she wasn't in the show.
I think about what they put the adult female actresses through on those shows and it would break my fucking heart to have a young teen girl put through shit like starve yourself to get you to fit into a costume, worrying about your looks, go put on a padded bra, being the fantasies of adolescents and adults alike.
And then the audience hates you anyway because you're too smart and you're a girl, or at least that's how it comes across to you, so you leave the show depressed and just completely wrecked.
No thanks.