I love Brazilian Jiu-Jitsu (BJJ) and Yoga. However, I think people need to understand a difference between exercise and sport. Exercise has a regressive and progressive quality that distinguishes it from sport. When you exercise the goal is to find a move that you can do easily enough to repeat but challenging enough that after several repetitions it becomes a stimulus for change or adaptation. For example ,there is a weight that you can squat 10 times but no more and if you squat that weight for a few sets of 10, you will stimulate your body to adapt and get stronger. At that point you need to progress to more load or more reps in order to keep getting stronger. Thus the goal is never to master the 10 rep squat at 95lbs. The goal is to keep getting stronger, faster, better, etc. and do with 195lbs what was once only possible with 95lbs.
When we do a sport like BJJ or Yoga (I know yoga is not a sport, but more of a practice, however, people mistakenly treat it as exercise), we initially find it very physically demanding. Thus it does creates a stimulus that drives adaptation exactly where we need to adapt with respect to the sport. We get stronger and more flexible and our stamina increases and we can train longer and better. Initially people think that all they need is that one thing, BJJ or Yoga, for all their fitness needs. They mistakenly believe that they will keep getting stronger and fitter just by doing BJJ or Yoga. However, the difference with BJJ and Yoga and similar sports is that as we improve at them we actually learn to be more efficient and can perform better without spending the same energy that we did when we first started. As we get better we cease to adapt physically.
Watch a novice and an expert perform the same moves and you are not struck by the physicality of the the expert but rather the ease and fluidity of their movement. Your first few months on the mat, you use a lot of energy to attack and defend against your opponent. Your body adapts quickly to the stress of BJJ and then you are able to train with less difficulty. After a short time you learn to relax as you train and exert energy when you need to and conserve energy when you can. When you reach that stage, it is rare that your BJJ training becomes a physical stimulus. What you start to develop is neurological aspects of technique such as timing and coordination by repeated repetitions and focusing on details and positions. As you advance, Yoga or BJJ training becomes skill practice and at that point in order to stay physically sharp, you need to supplement your BJJ practice with outside training exercises, so that you continue to gain in strength, stamina, speed, power and flexibility.