No it's not good. I can't think of any advantage with being flat footed. In boxing you need to move constantly. Small steps, small movements all the time. You can't just stand there. You present an easy target. I don't understand why you would ask if you would a good fighter. Your coach is yelling at you because you are doing it wrong and you ask if it's ok. It's not ok. Fix it.

Make a habit of walking about on your toes.

It'll build strength in your calves and if you ever get the chance to train barefooted it will make it easier to understand the concept of gripping with your feet.

It's a rookie mistake. It wore me out at first but now I don't even notice after hours of fighting...Like other people said, more agile, more sturdy, and much quicker

No. You'll be slower and less agile. That's why your coach is yelling at you. Because you're doing it wrong.

My boxing coach always yells at me for being flat footed. I don’t feel right on the balls on my feet. Every time I’m on the balls on my feet I get tired faster than when I’m flat footed. I hold a purple belt in bjj under Rickson Gracie and working on my stand up game. Will I be an okay fighter in the MMA and boxing world in a real match by being a flat footed?