This is as much a comedy as the Illiad was in that sense however, as we aren't poking fun in narrative at it, there is no exaggerated traits of the Imperium being displayed, The Culture in story is seriously trying to answer these problems and reform peoples lives.
Hamlet had comedic elements. The Diary of Anne Frank, had comedic elements. Having comedic elements does not make it a comedy. Saying that it does is much like saying Gallows Humor makes a hanging a celebration.
As for Orks, the consensus was split, and it was decided to have a full half of the ROU's / GCU's decide to wipe out the Orks. I'm pretty sure that means that they're all but gone.
The problem of Orks never existed, because it was never a pressing issue.
The tyranids were immediately answered, the IOM's governmental reform is prioritized lower than answering the threat of Chaos in the store.