Heh, these days everyone's an art critic.

The blaster bolts are supposed to be coming from more than just one gun, there is another Rebel up there near the one you can see muzzle flash from who is also firing. The blast explosions were part of the original image and in my opinion add a nice level of intensity to the scene, showing the onslaught of weapons fire that the Sandcrawler is enduring from the Imperial attack. All just a question of taste.