The Klingons in Star Trek are unpleasant because most Klingons stories are about making peace. Making peace with nice people is easy. Whereas, most Romulan stories are about the humanity of our wartime enemies. That requires a more rounded portrait.
If Moore didn't get this, he was rather obtuse. Also, if he didn't understand that the passage of time or a broader sampling of alien characters permitted variations, he was rather obtuse. He seems to be thinking that being of a species means there is a certain character, a kind of supernatural essence, expressed in all members. That is a deeply reactionary idea. Combined with Trek's tendency to treat species as a metaphor for race, it shades into downright bigoted.