Working out at the park is great, but the park in itself is equipment. It may seem like it was free but actually it is not, we already paid for the equipment with our tax dollars. The commercial gym is like Barnes and Noble, the park is like the public library.
Can't afford to buy books, then go to the library, but if you can go to both that would be ideal. The library will not carry Osho books but you will find them in the bookstore. Nobody can ever argue that a simple pull up bar is not a useful piece of equipment for fitness development. Hannibal using those bars, that's equipment! That equipment was built with tax dollars.
Training with absolutely no equipment would include no pull up bars, no dip bars, nothing, just your body. If it's just your body and nothing else, you will have an imbalanced development; you will lack the muscles of the back mainly. Even climbing a mountain, that serves to be equipment. Not everybody will live by mountains to climb, so they will build bars to get the exercise.
Running outside full of pollution may actually hinder your health compared to running on a treadmill at home with cleaner air. I've train with equipment and with no equipment, I've learned to love both, both is important, we need to be developed on all realms.
Training in Parkour compared to a gymnastics gym can be very dangerous if you do not know what you are doing. You can crack your head open doing some of those flips. The gym can be a safer way to develop yourself to prepare you to be able to perform such stunts in an open environment.
We can lift rocks as a way to exercise or we can use the modernized development of dumbbell weights or plates. Rocks may not cost us money but lifting rocks will make it difficult for us to balance our training, as we will not know the true weight of the rock, in order to weigh the rock, we will need to use more technology, the scale. Rocks will be difficult to grasp and allow us to hit different angles on different exercises.
Also there are MANY people out there who cannot even perform basic callisthenic movements, such as the pushup. Someone that can’t even perform a pushup will find it very difficult to build the muscle groups associated with that exercise. Therefore they will benefit greatly from the use of equipment that will prepare their bodies to be capable of performing the basic pushup.
For example a man who weighs 200 lbs who cannot perform a pushup can work on bench pressing a 45 lb bar in order to develop his muscles to be capable of pushing up his own body from the ground.
For the elite, callisthenic exercises in itself just is not challenging enough. Someone who can do a front level for long period of time will find it much more challenging if you had him strap on 50 lb ankle weights and try to do the same thing. Hannibal for example seems to be superhuman doing certain fitness feats, but have him strap on a 100 lb vest to do the same thing and you will see that he is no longer superhuman.
A marathon runner who thinks he is so fast, well have him strap on a 100 lb vest and see how fast he is then. Equipment can serve to either prepare us for the basic body movements of exercise or it can help us go beyond the basics. We should not turn against equipment nor should we be dependent on equipment. We need to be proficient with and without equipment.
Equipment does cost money, but if you have an abundance of money, there is no problem. It is only when you have no money that you will have to seek for more affordable ways of achieving a high level of development.