Class and honor are two different things.
You seem to fixate on how he treated Dante, but forget all the other things he did.
-He tryed out his new devil arms on a dead demon courpse just because he felt like it.
I can't argue there it was pretty cruel
-He went against his code to use guns. (Though it wasn't a code, it was just his pompous beliefs of not using guns)
Recently I've been rethinking about how I see Vergil imo I think if Vergil had the choice he wouldn't use guns because he would rather fight someone head on then at a distance but he knows how to use a gun
-He was selfish and only wanted power even if that meant killing off humans.
He seemed pretty neutral when it came to humans he was willing to put up with Arkham for who knows how long and was pretty tolerant to Lady when she was trying to kill him, when the demons came out of the teminigru yeah he wasn't really concerned for the humans safety but neither was Dante
-He butchered a bunch of thugs in an alleyway in the DMC3 manga.
Yeah, It was pretty much overkill and again I can't argue with that but he did decide not to kill Enzo when he was drunk
-He isn't very chilvery since he straight up calls Alice in the manga a whore.
But she was...he was more blunt on that note and Alice was pretty annoying as a character and served really no purpose in the manga
There are many words to discribe Vergil. Honorable is definitely not one of them.