Oscars are more predatory than aggressive their true danger lies in their appetite. some may show true aggressive behavior but this is usually mild when compared to many other cichlid species
I've had two Oscars. They both try to use their size and bully other fish, but if the other fish push back - Oscars turn tail real fast. Obviously some are more aggressive than others - but for the majority I'd say they are mean mug marshmellows.
Oscars arent wimps..what da' heck!!!!....everything is relative.. if I come up to you with a fully developed and starving Channa micropeltes then almost every fish is gonna end up being a wimp.....