Banting certainly deserved the prize. He had the unique experience, only a true scientist can experience, of knowing the answer to a question that stumps others. Macleod never experienced this with insulin. However, Macleod was certainly an essential player in the useful application of the discovery of insulin. Without Macleod, even if Banting had somehow found the laboratory facilities to perform his experiments, the best he could have achieved was writing a scientific paper in an obscure journal that would be forgotten. The true importance of the discovery only came about through the administration of insulin to human patients.
Banting’s specific idea, the tying off of the pancreatic duct, was obsolete within a year. It was simply impractical to produce insulin on a large scale using this procedure. Macleod realized this early on and took steps to isolate insulin other ways. He suggested Collip work on the biochemical purification of insulin. He also pursued the idea of isolating insulin from fish. In fish, the digestive and insulin producing functions are physically separated. This made the separation of insulin from the proteolytic enzymes easy. However, the biochemical purification worked well enough that he dropped the idea of isolating insulin from fish.
The three main people involved in getting insulin to patients were Banting, Collip, and Walden. Banting isolated insulin in a dog, but his isolation procedure was not practical for human use. Collip developed the alcohol method of purifying insulin from pancreases. Collip’s innovation was sufficient to keep a dozen or so patients alive for a few months at a time, but could not be scaled up because he did not realize the importance of controlling the pH of the solution. Walden made the key discovery of how pH effects the solubility of insulin. Walden‘s optimization of the isoelectric precipitation of insulin provided tens of thousands of people with insulin to live their lives.