Conversation so far:
Where did Pierre Boulez begin his musical education in 1943?
In October 1943, he auditioned unsuccessfully for the advanced piano class at the Conservatoire, but he was admitted in January 1944 to the preparatory harmony class of Georges Dandelot.
What was Pierre Boulez's primary focus under Georges Dandelot?
preparatory harmony class
Did Pierre Boulez write any pieces during the time at the Conservatoire?
Did Pierre Boulez receive any special recognition as a student in the preparatory harmony class of Georges Dandelot?
His progress was so rapid that by May 1944, Dandelot's report describes him as the best of the class.
What did Pierre Boulez do after winning the best of the class in Dandelot's report?
Around the same time he was introduced to Andrée Vaurabourg, wife of the composer Arthur Honegger, and between April 1944 and May 1946 he studied counterpoint privately with her.

Question: Who had what he felt was a lack of imagination?
Self-contained rewrite: Who had what Pierre Boulez felt was a lack of imagination?