Kevin Smith is a one hit wonder. He hasn't really done anything great outside of his first movie, Clerks.
Similar arguments could
be made with Joss Whedon. It could also be argued that Smith's "Dogma" had a measure of success or notability and he certainly has a good fan following.
And given the... "unusual" restrictions he was under for doing the "Superman: Lives!" script it's not too bad. His Batman comics aren't bad either and certainly introduced a very interesting villain (Onomatopoeia.)
Disagree. Whedon has shown much more talent with Buffy, Angel and Firefly along with his background as a comic writer before he made it big with The Avengers.