Ever wonder how good Lucille Ball could have been if it weren't for Dezi and the success of their tv show? She was really beautiful and a fine actress. She would have give a lot of female stars a run for their money, not to mention the men.
Considering that she was a working actress for 20 years prior to "I love Lucy," I'd say that the show had nothing to do with what you seem to perceive as her not making it "big".
Of course, I'd also argue that you're highly mistaken. Lucy, who was the first woman to run a major production company, and had numerous roles in film and TV, was a "Star" in every sense of the term.
She was really lovely and you can see in this movie that she had a truly gorgeous figure (oh those dresses! Beautiful!) -- but after 20 years Desi and "Lucy" came calling and it was a perfect fit for her timing.
Also, you have to remember she was entering into "that certain age", no longer in her twenties but still young enough to have babies. I believe Lucy did very well.
She was already prepared for I Love Lucy with My Favorite Husband. Not sure her legacy would have been as strong without ILL. So many actors/actresses had long good careers in the movies but really had staying power when landing THE tv role. I think of Moorehead in particular with that.
I've never cared much for "I Love Lucy" or any of Ball's other comedy tv projects. But she was very good in "Lured" and I wish she had done more movies where she played realistic, intelligent, fairly serious characters like this one.