Any characteristic, including aggression level, can likely be magnified or reduced by carefully controlled breeding that targets that particular characteristic. But generally speaking, we do the exact opposite regarding aggression. The standard tactic for breeding most cichlids is to buy a small group and raise them up together; once they pair up, the losers in the find-a-mate sweepstakes get rehomed and we wind up producing spawns from the biggest, baddest, meanest, most aggressive, most assertive pair of fish in that original group. If you are trying to breed out aggression...this is the wrong way to do it!
Aggression vs. predation is simply a matter of semantics. A 12-inch fish eats a 3-inch fish, and his keeper says that it is aggressive for doing so. While that fish might indeed be aggressive, the fact that he has an appetite and eats food is not evidence in support of that description. Google "hungry".
And finally...as in all things...everything is relative. Back in the day Oscars and Dempseys and Green Terrors were considered aggressive fish; that was mainly because most keepers had never seen a truly aggressive fish. I absolutely do not believe that an Oscar today is any different from a behavioural standpoint than one from 50 years ago...but try to keep that "aggressive" Oscar with a Buttikoferi or Managuense or almost any large CA and you will have your eyes opened to a harsh new reality.