This looks like gross mismanagement. Gross mismanagement of client expectation, gross mismanagement of product scope, gross mismanagement of feature/engineerin

This looks like gross mismanagement. Gross mismanagement of client expectation, gross mismanagement of product scope, gross mismanagement of feature/engineering processes/schedule, lack of leadership, and worst of all, gross mismanagement of talent. It sounds like management has no or very little technical background. Didn't understand how to build the product or translate requested features into feasible functionality. And simply thrust the whole problem onto a single senior developer. The guy while talented was overwork and exhausted. I would turn into a Mr. Hyde too if I have to work seven-day weeks, twelve hours a day.