Have you seen this Key and Peele video: https://www.youtube.com/watch?v=CUvFeyGxaaU ?
I think it pretty much sums up why some kids end up as bullies. Look, same as you, I was bullied in school. In middle school, there was a time when I was sick to my stomach every day and afraid to get on the bus in the morning. I got pushed around and teased, someone even wrote on the side of my house in red paint. For years I thought it was something about me that made me target. It wasn't until I was an adult that I realized it wasn't about me at all. Lots of kids get bullied. In fact, I think pretty much everyone gets bullied at some point or another. Being bullied doesn't mean anything is wrong with you, or different about you, or that you're inferior in anyway. The reasons for bullying are all about the bully, not the victim.
Bully's are not kids who think they're coolo and better than everyone. They're kids with fucking problems. Like, have you ever been in Walmart and seen that mom yelling "Get over here before I beat your ass" at her three year old? That's the type of kid that becomes a bully. The kid who's older brother beats the shit out of him for getting better grades than him. The kid who's dad is in prison, who's mom is high all the time and has her scary crack head friends over the house all the time, the kids who's own friends make fun of him, the kid who used to have a lisp, the girl that's taller and heavier than all the other girls in class, the kid who's too poor to have the clothes that everyone else has and feels so inferior that he decides to steal your shoes, and so on and so forth. People aren't just born bad. Life is unfair, some people get a shit deal, and don't have the coping skills to deal with it. So they bully others as a way to alleviate the pain. And that sucks. For them and for you.
I think the reason everyone loves a good revenge story is because it's nice to fantasize about a world where there are "good guys" and "bad guys" and everything can be worked out easily. Good triumphs over evil. That's satisfying. Real life is not as satisfying. Sometimes bad things happen to people and the culmination of those things turns that person "bad". Realizing that is frustrating, because it takes away the satisfaction you get out of hating them. But I think that's the path to maturing into a well balanced person.
Like you, I've gotten some satisfaction out of learning to be the intimidater. But don't let that become who you are. If you were really over the bullying you got, you would realize that you don't need to do anything to get "back at" your bullies. Some people say "Living well is the best revenge" but you don't even need to do THAT. I don't think it's healthy that you've been so motivated by your bullying. You don't need to do ANYTHING at all. You don't have to prove anything to anyone. Whatever people said or thought about you doesn't matter. Live your life for yourself, period. Get jacked at the gym if you want to do it, but don't do it because you have something to prove.