Well, with zero offense of course you have no score, so winning is impossible. A flip answer, but true.
But that doesn't mean that defense is unimportant. In all sports -- and here I am specifically thinking of an NBA team from, uh, 15 or so years ago (out West, and I am totally blanking on which one it was -- Dallas?) which would routinely score record-breaking point totals, high hundreds -- and was routinely beaten because their opponents would score more. They scored like crazy but were a lousy team and I'm quite sure that they did not make the playoffs.
Now, basketball and football are of course not the same beast but I think the principle applies accordingly -- you need both, and extremes in either direction tend to make you a mediocre team and not a great one, despite what can be some rather impressive individual accomplishments.
PS I suspect that a lot of teams with imbalance in one direction or another may also have team chemistry issues, e. g. one person is a star, whether offensively or defensively.