Everyone that teaches feels that way at times. Does not make it any easier to go thu but your not alone.
Jonwade above put it very well.
"Their asperations may not be to be the enxt instructor, but to be just the best they can be within the time that they can afford to set aside for the activity."
Then again, your the guy on the ground and you would know better than we if they were slackers who want the rank without the work.
I did battle with ignorance today.......and ignorance won.