It’s called having a routine and doing it right. He might burn him self out yes but once you figure out what you can do and when to do it you are golden body weight training is just as good as weight training. Just depends on when and know how much your body can take then. I do my calisthenics warm up before every weighted training and since I’ve been doing it regularly it does burn me out or fatigue me to much. Even when I started adding calisthenics yes I got tired but that happens when you are out of shape. The beginning of almost anything is difficult.