Well, I thought that I had posted enough on this thread until reading your post, just above.
There is an old saying that, “In the land of the blind, the one-eyed man is king.”
Those incompetent teachers, of whom you write, have helped produce at least two generations filled with nearly “blind” citizens. And the state and national capitols are full of one-eyed “representatives.”
FWIW, the class my wife teaches is at a local Community College. Apparently, it's a well-regarded program, at least locally.
I asked my wife, "Why do you pass teachers who can't add, can't tell time, etc?"
Her response? "I can't fail 75% of my classes. This is a childhood development class, therefore there's no room in the schedule to teach basic math to 20- 30- and 40+ year olds. So, I judge them on more subjective standards, like, are they good with kids, would they make a good hire for a daycare, etc etc etc." She fails a few, and in talking to her, it sounds like the real zeroes pretty much weed themselves out.
I can see the dilemma. When you're presented with students that have "graduated" HS, who have been so utterly failed by the system and can't perform some of the more simple tasks .... what do you do?
I just don't have a frame of reference for it. The washout rate in my engineering degree was something north of 2/3rds. And in my job, there's very little wiggle room for "meh, close enough". Either the system works, or it doesn't. And I don't have someone going behind me to double check and correct my work or say "Well, your mistake cost the company 5 million dollars, but that's OK. You've been on time most days and participated well in all of the meetings."