i never pictured you as a priest of mass generalization.
seriously, saying mirrors are an illusion for beginners may be true based on your experience, but it is not true for everyone's experience.
Strength training is mountain biking is baseball is football is running is everything.
The act of watching yourself do something in the moment is lost on the beginner. When you put your finger on someones lats while they're rowing they'll get more benefit than a year in front of a mirror.