I don't think they "broke" Johnson, they pushed him but that's part of development, Kemp got pushed to AAA too fast, but the experience probably will help him next season.
There's a difference between throwing a player over their head to start a season, and giving him a taste of adversity at the end of a season to prepare him for the off season. The first can crush confidence, the later, motivate off season workouts and study.
Johnson wasn't ready for the majors and probably is fatigued, but he now understands he can't just throw hard to get ML hitters out and that he needs to be in better shape to handle starting for a full season.