The twin sons of Sparda are not heroes. Both are the polar opposites of a hero.

Dante is a mercenary who takes jobs that consist of him slaying demons for profit and he ignores jobs he doesn't think are worth his time or would pay well meaning he's probably indirectly gotten someone killed and he couldn't care less.

Dominic is a mass murderer who got off scott free due to him being one of the strongest people on the planet and even to this day he kills the heroes who try and end his "tyranny" even though he just wants to be left alone.

Now, they aren't morally bad people, Dante could've just told Patty to pound sand even if he would've gotten paid, but he's not that kind of man. Dominic just doesn't believe in killing the undeserving unless they give him a reason to kill them. Dante has given him many MANY reasons.

Dominic has even turned the Decepticons from warmongers to a PMC/Mercenary faction ever since he took over as leader and became king of the Underworld. Even if Dominic does blow up a town or two. But he has a giant warship and you don't so NYEH!

???: I need more power!

Dominic: Who said that!