I really am not seeing the big deal with this video, it seems like common sense to me. Make sure your dog is conditioned, weigh the benefits and risks, evaluate if your dog has the physical make up/ability to do an activity.
This is something that is commonly discussed with horses. If you want your horse to do a certain strenuous activity and stay sound for years you make sure the horse has the correct confo and conditioning for said activity and know when enough is enough. If a horse say, refuses jumps repeatedly, the first thing that most trainers recommend is to make sure the horse isn't refusing due to physical pain.
She is not telling people to never do anything fun with their dogs, she is just recommending people use their brains when they do it. Plus, many dogs don't know their limits physically and WILL work through pain. Jack has DJD in his elbow due to elbow dysplasia. He had surgery when he was 10 months and it took him years to figure out his limits, and often he still has to be reined in. I also agree that having your dog do downs where they are repeatedly slamming their elbows onto hard ground is not good for the joints. Jack's physical therapy vet also advised to that doing things that would repeatedly stress his front legs with repetitive jumping, slamming down, etc, was not good for him, so I choose not to even attempt agility with him. I would gladly do agility with future dog though. It's not about wrapping a dog in bubble wrap, it's about taking the individual dogs physical condition into account when doing physically demanding activities.