By 1944, the shape of Namor’s head has evolved in an increasingly bizarre triangle-shape direction, as seen by the panel above from Sub-Mariner #13 (April 1944). His body has also gotten considerably more muscular, but his head really makes it hard to take him seriously.
Two-and-a-half years is a short time for the look to change this much. Like just what is this nightmare moving towards me in the water?!?