The shields do not steer weapons fire away from the ship, they exist solely to block weapons fire in all forms. The Vengeance has weapons that seem to have homing ability, maybe the phasers are using some kind of positive energy that is attracted to ship hulls or energy signatures. After Big V nails the Enterprise out of warp we see it blast Enteprise again but with straight phaser bolts instead of curling bolts. You have to remember that this version of Trek has absolutely no technical aspect so we're never going to know exactly why these weapons do what they do. The drone came out of the ship's side, both sides have a row of rectangular and circular hatches which can be seen on the Hot Wheels replica and briefly after the special torpedoes blow. I think the rail-gun torpedo launchers are on the belly somewhere since Marcus said aft torpedo launchers, it would make little since for them to be on the saucer if they are "aft" weapons and it showed a second one deploying adjacent to the original shot.