Many years ago, my wife did some geneology research and found that we are probably related through Daniel Boone's grandfather. My son, 16 at the time, wanted to know if that made him a redneck?
Not all sex links are small. Some hatcheries sell commercial egg laying chickens as sex links. These are generally small. Since they are commercial egg laying breeds, they efficiently have most of the feed they eat going to egg production instead of having to maintain a larger body. Some hatcheries cross two dual purpose breeds to make their sex links. These birds will be the same size as other dual purpose breeds. Some of us make sex links from the breeds we have on hand. These can be any size.
Not all bantams are the same size either. Some are a lot bigger than others.
I agree, a bantam rooster will try to mate a full sized hen. It does not always work. but they are more often successful than many people give them credit for. The more difference in size, the less likely it will be successful. It is not a yes or no question, but more of a maybe.