King Kong wringing a bunch of giant chicken's necks wouldn't sell. He'd be like a giant... farmer, or something, and not a giant 'gator rassler', which is considered more dangerous, I'm sure.
Seriously though, birds are pretty cool, with the talons and sharp beaks well suited to the hunt, excellent eyesight and hearing in some species, and lightning speed. The idea that a branch of theropod dinosaurs became birds is cool, and a window onto some of the possible behaviors, if not cosmetics, of these earlier links. But that's science, I guess.
As for the visuals for a movie, scales or dino skin = monster; even eagles and other larger modern birds have a 'lightness' about them, probably derived from the ability to fly, that doesn't imply 'bruiser' in the same way as a monitor lizard lumbering into view. A large pissed-off modern bird can be scary, but Salties look like pissed-off armor-plated reptilian eating-machines; visually, the latter was always the better way to go in terms of intimidation.
Can birds be scary? Sure! But I just think it's easier to go the reptilian route to get an imposing look, and since I grew up with that visual, it will always carry more weight for me.
