And, of course, ships have navigational deflectors to shunt all the small stuff out of the way (and 'small stuff' includes everything from dust to asteroids). Any bodies larger than that could be detected far enough away to navigate around.

This is one of the problems. why didn't the Enterprise know it was decelerating into a debris field of wreckage?
In the first Star Wars movie, Hans Solo decelerates into the debris field that was the planet Alderaan, it was a surprise because he and his ship were traveling blind. The Enterprise doesn't travel blind. Or shouldn't be, we've seen the Enterprise go from warp to impulse and rendezvous with a sublight ship, they knew it was there because while at warp the sensors showed a ship not at warp. If Captain Pike was going to drop to impulse into a formation of Starfleet vessels, he would need to know where they were. The sensors didn't detect the wreckage. They dropped into orbit blind.
Even if Nero hadn't destroyed the fleet, Pike and the Enterprise still would have been in danger of colliding with another Starfleet vessel.
When the Enterprise arrived in Vulcan's orbit the wreckage of the fleet was slowly dispersing. There were no remaining visible fireballs. The Enterprise may have left Earth's orbit 44 second behind the fleet, but it seems for whatever reason they arrived more that 44 second after the fleet arrived. Perhaps because the Enterprise was a brand new ship, maybe even on it's first long range cruise, on the trip to Vulcan she gradual lost ground to the rest of the fleet. The Enterprise arrived several minutes late, The wreckage wasn't wildly flying apart, but at it's slow speed of break up it had time to spread across a few miles of area.