I think I got your idea. By getting the importance/time density, you might get more tasks done and increase the overall important score. This is a great idea.
What I am trying to contemplate is that would this help us to focus on increasing productivity? To answer this question, it really depends on our definition of productivity. Since my definition that I have in the problem for productivity is to complete the important tasks, not to complete as many tasks as possible, the results give me what I want. But I like your idea of getting the density and I will think more about this. Thank you for your helpful suggestion.