Two things.I can't imagine Greengrass and Damon making a bad Bourne film.
One. Would you agree Bourne Identity was the best of the original trilogy? Well Greengrass didn't direct that one.
Two. Since the trilogy other franchises have stepped up their game. Look at the latest 007 films for example. And Nolan's Dark Knight trilogy. The new Bourne is no where near those levels.