Ask someone who has actually hunted there before you start making unfounded judgements. The deer are smaller because they are desert mule deer. Genetically they are smaller in body stature to be able to shed heat. The opposite is true for Northern muleys. IMO however, the bodies are still not that small. The buck I killed weighed about 100 kilos. It sure didn't seem small after carrying him out whole, lodgepoled over a palo verde, for 2 kilometers in that country.
True, their are a few high fence ranches, but far more are open range. Most are as fair chase as it gets. Cattle is a huge industry in Sonora and most spreads are working cattle ranches.
The hunting is not your steep, high country above the timberline stuff, but it is difficult in its own right. You are tracking bucks in very thick brush, in pretty flat country without many high glassing points. You really have to have some woodsmanship (maybe cactusmanship is better suited) to get a shot at these deer. And when the shot comes it will most likely only be a split second opportunity before the deer vanishes. You have to decide if that is the buck you want, and then figure out how to make the shot, all at the same time.
The magazines and shows make it seem like 200" bucks are under every mesquite tree. Nothing could be further than the truth. I hunted with a very prominent outfitter (who is a friend of a friend) and he told me that guys who come there expeciting to walk out and kill a huge buck within a day or two will be sorely mistaken. He said that success is about 50% for a week-long hunt and a lot of those are "only" 160-170" bucks.
But the true beauty of hunting in Mexico is not the huge bucks. It is the mystique. The wonderful people, the living on a remote rancho, the sunrises over the Sonoran desert, the great food, and the step back in time. That is why I can't wait to go back.