Bigger movies? Saldana was the female lead in Avatar, which is the highest-grossing motion picture in the history of the world,
Hidden behind CGI. They could've stuck any actress there and I doubt it would have made any difference.
That's not even close to being true.
I would suggest watching a few behind the scenes featurettes on how they do performance capture for these things and how integral the actor's work is, especially in something like Avatar or the LOTR/Hobbit movies.