So much error here. "By his stripes you are healed" doesn't refer to physical healing. It refers to spiritual healing. God doesn't promise us physical healing or success or prosperity or wealth. You certainly must have seen sick people that don't get well. A lot of them die. Especially old people. My first wife died from kidney disease when she was 30. She had a lot of people praying for her too.

In the New Testament Paul had bad eyesight. Timothy was frequently sick. Christians don't have better health than nonchristians.