You think DmC's guns are underpowered, seriously. You're joking right. DmC's charged shots are ultra powerful, insanely powerful, ricoshot interrupts and breaks deviltrigger on all enemies, it's how you can handle multiple targets without having your combo interrupted. You obviously played DmC very casually and ddin't actually experiment with the effect of guns and how they help in managing large groups of enemies.
Fireworks spreads out enemies in nice 45 degree cones for easy targeting, ricoshot interrupts enemies so you don't get hit by pesky harpies and sky rats, kabloeey causes splash damage that also sends enemies flying in different directions, same thing for skilled release shotgun bombs. Rainstorm gives you plenty of height and style points, which is kinda the main thing DmC is about: doing battles with as much style and creativity as possible.
Watch the power of ricoshots.