I have an 800g tank and at one point had several peacocks, an arowana and four giraffe catfish in that tank. They all got along well enough to be long term tank mates. A few years ago I dropped a Fireman's Dream in that same tank watching for aggression levels and having no clue what to expect. The FH was painfully small in comparison to the peacocks and you've no doubt noticed that peacocks have a 'win at all costs' feeding manner.
If I had a fear it was that one of them would get tired of the FH's crap and beat the holy hell out of it while I was away sleeping.
Uh, no. The FH did not care one bit about size difference and would happily take on any fish in the tank just for fun. Eventually all the other fish in the tank stayed in one quadrant and the FH had the other three, occasionally venturing into Q4 just to be a complete nimrod. I found myself wishing that one of the peacocks would run up to that idiot and give him the mother of all bites, chew his stupid ass up and spit the carcass out onto the floor but nope.
FH's have a problem w/ constipation and it was initially in the back of my mind that I should keep an eye on him, keep enough flow that he had to exercise a bunch in order to keep his pipes clean, etc. I could put plenty of flow in the tank but at feeding time he would hang out wherever I was and eat everything. Zero chance of the others getting any food until that little clod had had WAY too much.
I paid a lot of money for that fish and eventually took it back to the shop I bought it from and said 'enjoy'.
I'll never have another.
If one were forced upon me I wouldn't expect it to be respectful of tank mates. Eventually there will be blood.