This is written in the context of golf conditioning, but the take-home point applies universally: "core" training is a gimmick.
http://www.medfitnessprogram.com/service/blog/2015/04/16/golf-fitness-blunder-1-core-workouts
Richard J. Wolff, RD, LDN
Golf Fitness Blunder #1: Core Workouts
If I had a nickel for every time an athlete said to me “I need to train my core” I would be quite wealthy! “Training the core” (abdominal muscles, back muscles, etc.) has seemingly become the solution to every sports performance problem. As it turns out, “core” isn’t even a legitimate medical or physiological term — the word was coined by Reebok as a way of promoting fitness apparel.
Training your core at the expense of other muscle groups is a big mistake. Many golfers do have a weak core - but they also have weak shoulders, hips, quadriceps and hamstrings. In other words, muscle weakness often exists within the entire muscular system, and training your entire body (not just your core) is the best approach to improving your golf performance.