I'm just gonna come out and say it, I find DMC2 the hardest of the series when not trying to overuse guns. Some of the enemies are quite tricky (like the flying goats)
I think it's amongst the hardest because I have a hard time staying awake. But true that, they kinda made many flying enemies in the game, and with the aerial controls of your melee weapon being quite bad it's tough.
But that's like, artifical difficulty as people say. Fight birds only using earthquakes when you might as well throw things at them.
It's more like they built the game around the fact that you are going to be shooting, and you are going to be shooting alot. Like the infested helicopter, or the bosses which constantly uses pushback abilities as soon as you get close, or the massive space around most things.
So not using the guns wouldn't make the game hard, just more tedious or annoying.
Worst thing of all, style keeping is incredibly easy. Hit a sword combo, spam guns and keep your style at its level as long as your hitting something, walk to the next nearest enemy, dash in for a combo, then spam guns, never losing the current level of your style bar.