Nearly every agency I've ever been sentenced to has had a tussle or two about how crappy their briefs are. They blame mediocre work on mediocre briefs. The fulminate and put together committees on creating a better form. They then demand a certain scrupulousness on creating briefs and so on.
I believe in the brief. But there is something way more important. That is the absolute drive to do work that people haven't seen before. That informs, moves, entertains. It's really that simple. Do something good. Have the leaders of the agency sell daily to the client the need to breakthrough and be different. In short, the briefs we should be fighting over are not the individual ones for ads on the "$49.99 Call Your Fucking Estranged Mother Plan." The briefs we should be fighting over are simpler: Who are we as an agency and what do we do? That's the only brief that is really important.
