Kinda interesting topic. I had a Kole (yellow eye) Tang that was a total A-hole. Normally a super mild mannered fish, but this guy managed to kill a couple Blue (Hippo) tangs, a Blonde Naso, Foxface Lo among others. To distract him, I added 5 Yellows, a Tomini and a Purple Tang all at the same time to my 240 (900+L) tank. Since then, he has been a model citizen.
Fish are people too. All have different personalities. A normally mild mannered fish can be a d!ck, or conversely an aggressive fish can be a total sweetheart. Having enough room/territory, feeding a proper balanced diet for any specific species of fish, can go a long way towards success mixing conspecifics. Although not always a given, it can be done. Oftentimes, with great success.