WOW!!! couple things
1 Fish are wastfull. Many(not all just many) will not tolerate certain fish or (like mine) will kill and not eat the body. When a Oscar kills a chilicd is this not wasteful? Cichlids are terrorital and rarely kill other cichlids in the wild but in aquarium where they cannot escape from the aggressive cichlid. Even their own mate unable to escape from the male because she cannot get out of the aquarium from her own mate. it is the owner's responsible, not nature's responsible.
When a Blue whale catfish burrows inside another fish kills it, just to only eat a small amount, is this not wasteful? Again this is in nature, not in aquarium. Blue whale catfish are not only scavenger, other blue whale catfish, small fish, snails and leech will join to eat the dead fish as nothing's getting wasted in the nature. In aquarium, there are no scavengers, just snakehead and nothing other.
When a Gar(maybe mine is the only one that does this but) kills a feeder fish knowing its too big to eat is this not wasteful?? How can you say fish arnt wastefull when there is great examples probably in one of your tanks.
Again this is not nature because we cannot mimic full nature in the aquarium.
2 fish think they are king untill a new fish asserts its dominance in the tank. Trust me i know youve seen this, we all have. Because they cannot escape from the dominant. In the wild, they can just move from this area to another area. It is not uncommon for the lowest rank cichlid become killed by dominant cichlid because it cannot move to another area.