Brevity can be (is) just fine, if it's what the table as a whole wants. Especially if you have players who particularly enjoy char-build, it gives them a chance to try out more ideas.Focus is fine, brevity is not, assuming you and your group are intending to stay together for the long term.
I'd say the players are contributing at least something in the direction of authorship, if the DMs are being constrained to run adventures that fit the PCs' needs/stories. FWIW, the campaigns I run (which I gather are quite different than the ones your group runs) behave similarly: They start with an instigating event which I write up, then future arcs tend to be based more on the PCs' actions and goals.interesting timing in that I and the other main DM in our crew have just started an email exchange regarding adventure roots: whether a given adventure is something the players pushed for, the DM put them in, or some sort of mix. Early returns show that as a campaign goes on and develops more internal history, players (and their PCs) become more likely to drive adventures based on things that have already happened. That's still not authorship, in that the players aren't writing the adventures; it's more that the players are to a degree forcing what the DM will run next as opposed to the DM simply deciding.