The really efficient meat "breeds' are all hybrids and don't breed true. Some people use them in breeding projects to try to develop their own breed of high production meat bird.
So, it just depends upon what you want to do. I like the Cornish Cross, so I just buy chicks. Even with purchasing chicks and paying shipping, I end up with a reasonably priced product on the table that is miles better than anything I could buy.
I already breed purebred ducks and geese and I have a turkey project starting. So I don't have time or space for any sort of chicken project. It might take you dozens of generations to develop a meat breed that begins to approach the efficiency of the Cornish Cross.
Some people enjoy the challenge of that breeding project. Breeding chicks isn't going to be much cheaper than buying them because if you are breeding your own, you must feed all of your breeding stock over the winter. Home raised chicks are not free.,