Interesting read but not true all the time. Any oscar, firemouth, or convict can be ferocious. Pick the most dominate ones out of a tank full of them, its simple. The dominate ones eat the most/best, they harass the others, and they usually have the most color.
To be honest, wild caught fish are 'almost' always pansy's. They would hide in or behind something in a tank for months.
I literally can go and buy a MEAN fire mouth and a MEAN convict from petsmart, only if I choose the most dominate one(s). Oscars on the other hand are bi-polar IME. They'll be fine one day eating and swimming with the other fish. The next day the oscar will fight, chase, and glass bang.
You never know, every cichlid has a brain of its own therefore you can't judge them all.