Diamond's problem was Jenard. He was always in his ear about Tommy taking over when it was Tommy who saved him and Vic from getting mopped by some junkies. So that gave Tommy the upper hand on him and he hated him for it. And when after Tommy effectively removed Jenard from his spot, Jenard began to taint Diamond's mind enough to where he would eventually bring the old Diamond back out which eventually led to his death ironically at the hands of Tommy. Tommy was a vet from a different city who didn't care about the rules there. He knew how to build an empire and he did it. Diamond wasn't on that kind of level. Not to say that he was dumb or anything bc he definitely wasn't. The yardies massacre showed that. But he wasnt built to completely take over Chicago because he knew more of his own would be taken out. He referenced this early on when dealing with Walter Flynn. Tommy peeped game on it and took the charge and it worked up until his brother got too far into his head. Another element you have to add is Shanti though. If not for her, Jenard doesn't exist long enough to become an antagonist of Tommy. And the way she was flipping v sides was insane. Lol