In my log line, the screenplay splits the focus evenly between Lester Burnham and the newly arrived Fitts family. But the studio reader's log line nails the movie we saw in the theaters. Put that way, the only possible answer is Lester. Now call me crazy but I have seen a ton of excellent movies that do not comply with this standard. As is so often the case, the issue does not concern the screenplay so much as the writer.
New writers play by different rules than established writers.
Ball was an established New York playwright. He paid his dues. He won the Oscar. Now he writes what he wants. Your screenplay has to tell one, clear, focused, interesting, intelligible story.