Perhaps the accusation of flatness stems from the ideal nature of
Faramir. It could be that Tolkien needed to have an exemplar of the
Numenorean ideal in LOTR to justify the distinctions between the lesser men
(such as the Rohirrim) and the greater men who are in a state of decline.
Aragorn hearkens back to that, and in the book he too could be called flat due
to his ideal nature. The film doesn't explore the different orders of
Men, so without that context, it would have perhaps been out of place to
introduce a character such as Faramir of the book. As with much in LOTR,
Tolkien found in writing that it had to go in a certain direction, and the
appearance of Faramir is one of those happy accidents that needed to be in the
book.
************************
"All wizards should have a hobbit or two in their care..."
