How effective are boxers in actual combat?

I have been studying boxing for less than half a year. A retired boxer in the gym can give free lessons as long as he buys gloves and protective gear and trains with him in the gym twice a week for about 2 hours each time. The coach's name is Xiong Wei. He is an old man about 60 years old. He is not tall, about 163, but he is very energetic. Although his belly is a little big, he still looks strong.

At first, it must be punching sandbags, practicing steps, adjusting breathing and so on. Two months later, one day, the coach said, today we are going to have a simulated actual combat training, and you will fight with me. If I hit you on the head, you will be replaced by someone else. A dozen strong men in their twenties began to fight with him. Some of them are 188 in height, others have studied for almost two years, and they are all fitness or boxing enthusiasts. Next is the coach's performance moment. We hit him with all our might. His big belly is suddenly as flexible as a snake, and all attacks can be avoided. Then when we were panting, he would shout "Bingo", and with a wave of his hand, he broke through our front frame defense, knocked us dizzy and ended up.

In this way, he hit a dozen boys in a row. He didn't catch his breath except sweating. On the contrary, we had a fight with him and couldn't breathe. And he has been holding boxing gloves, not wearing them on his hands! From then on, I understood the truth of keeping a low profile, especially for young people. Don't use your strong body to have casual conflicts with others on the road, or even start work first and call the police in advance. Otherwise, not only the police can't help you, but even the doctor can't help you.