So it can't be considered a RPG because it originated in the arcade? I agree it's a hack n slash game, but back then there wasn't a real clear cut definition of what a RPG video game was. At least not up until console and PC gaming came about.
I think it's as close to an RPG game that could be defined as such back then. Sure it wouldn't be considered a full fledged RPG by today's standards, but it does hold some key elements of an RPG nowadays.