I gave a good reason why the Legion characters should have been used instead of the Justice League characters. Young Clark...or Superboy if you will, had a long history of involvement with the Legion of Superheroes. I don't think that having them interact with him all the time would be a good thing but maybe one or two episodes per season or every couple of seasons would have been good. A two parter featuring the Legion right dab in the middle of season three or four would have been interesting.
Yeah the Smallville Clark has indeed been pushed and prodded and had people constantly telling him about his destiny. In fact it's become an injoke amongst fans I think of the show.