"fads" have ruined many breeds across the board in all livestock and pet varieties at some point in the last 200+ years. a fad can come in many forms. phenotype, genotype, show ring, performance, consumer demand etc. just to name a few. a top breeder never lets any of these things dictate the animals he is breeding, he breeds to suit his end goals for his personal use, if there becomes a demand for what he does, he never strays from his personal path. a good breeder will see many fad cycles pertaining to his animal of choice through his years. breeding percentages and coefficients are tools, much like epds for cattle, and sire and dam progeny stats for racehorses. all of these tools can be utilized to enhance your personal animals, but all can be abused.
the performance cow and hog dog industry hasn't even come close to seeing the fads that the horse and livestock industries have seen through the years...
here is a fine example, i find this page very informative as to the damages of indiscriminate fad breeding can do to your breed of choice.
https://www.msu.edu/~ritchieh/historical/cattletype.html
