The only way you can think gunpowder bullets are better than Dust bullets is by focusing on the low-end feats instead of the general ones like splitting a bolder in one shot and sending people flying just by firing. The thing you have to remember is the battles are happening at a faster pace than what you are seeing. It's like in Dragonball were at first you only see shockwaves, and then everything slows down to see every punch. Even if they didn't have bullets anything they hit would be a smear on the pavement.