I think the criticisms made by you and others of Dennett on all 3 points are fair. Let me start over.
The idea is that with a relatively simple set of instructions (forget the word "algorithm") one can construct systems that appear to be quite complex. What drew me back to this thread was my recent reading of The Superorganism by Hoelldobler and Wilson. It is a detailed examination of the "eusocial" insects like ants and bees. Some colonies have millions of individuals. These colonies have a division of labor with different "castes" carrying out different jobs. Each caste member follows a rather simple set of instructions. But at the level of the colony, there appears to be very subtle, complex behavior.
Some castes function the way our sensory organs do, they provide the colony with information about the environment outside the colony. Other castes receive this information and adjust their behavior (foraging, nest-building, reproducing, etc.) accordingly.
The GTD flow chart is something quite elegant. I know when I first laid eyes on it, it was like a revelation. I see a lot of people, after they experience GTD, trying to get some simple set of instructions for doing. Of course, doing is usually not simple. I think that Forster created instructions for doing that have a nice balance. They are simple enough to get the job done, but no simpler.