I read these letters as well, however did you stop to consider what he deemed difficult and your concept of complexity and difficulty may not align? There is a very small percentage of the player base that has completed 2nd Coil or all the ExPrimals. From a business perspective locking the highest percentage out of your customer base out of even more content is not the wisest use of resources.
Those calling for more extreme content do not even come close to the "other half" of the players out there, while I do like interesting game mechanics I can simply point out that the pros when presented with basically equal rewards will always go for the path of least resistance the majority of the time. Evidenced by how many insta-quits I saw in Pharos, City of Ampador, etc.