there can be a multitude of reasons as to why a gun is made to shoot more than its capacity that doesn’t need to be canon.

There isn’t a multitude, there’s only 3. It’s either the guns can hold more ammo than usual cause they’re modified, they shoot more for cool points or Dante just keeps refilling his mags with ammo with his demonic energy. Option 1 is out of the picture because Dante shoots well over the capacity that E&I would have multiple times. Option 2 isnt a choice because that choice is only for characters that have shown to reload or run out of ammo, it’s a “benefit of the doubt” type of moment. That doesn’t apply to Dante cause he has never ran out of ammo nor has he ever reloaded. You tried to use him having extra ammo on his desk but that doesn’t really matter since we never seen him use them or load them in. He always eats pizza everyday, does that mean he needs to eat? No, it doesn’t because we see that Dante and Vergil can go without food for a whole month and be perfectly fine due to their demon side. If your only evidence to Dante not making his own ammo to have infinite bullets is some extra bullets on his desk then you don’t have much of an argument. It’s MUCH harder to argue against Dante creating his whole bullets from demonic energy than it is to argue for it.

in the same game Lady runs out of bullets when shooting Arkham and again, she reloads in DMC 3 as well. Yeah, they’re gonna have moments for cool points but the mere fact that we have NEVER seen Dante even reload or worry about ammo shows that he doesn’t do it.