I think you have to find the humanity in the character and then the deterioration is a part of the process - the journey of the character. It's like playing King Lear. You can start off as a nice old man who finishes up crazy. ↗
King Lear alone among these plays has a distinct double action. Besides this, it is impossible, I think, from the point of view of construction, to regard the hero as the leading figure. ↗