When chickens mate the hen squats on the ground. This gets the rooster’s weight into the ground through her entire body, not just the legs. That way a rooster can be heavier than the hen. Roosters of the same breed are practically always heavier than the hens, sometimes quite a bit. Many people have full-sized roosters with bantam hens and don’t have problems.
But I fully agree, size difference matters. The more size difference the bigger the potential for problems. Some bantams are a whole lot smaller than others. Some full-sized roosters are bigger than others. Size difference is a good a point.
Mature adult chickens normally go through the mating ritual where it is not really violent. Not always but normally. The chances of injury are a lot less than immature cockerels mating immature pullets. With adolescents hormones are going crazy, the cockerels have not learned any self-control, and the pullets often don’t do their part so it can get pretty violent. That’s why age of males and females both is so important.