But none of that changes that new baristas can be trained to do their job in a few days and almost anybody can do the work.
If you take any person off the street and have them make you a cappuccino, you will absolutely regret it. But apparently you don’t believe this is true of teaching children?
All your evidence points to a much, much simpler explanation: most teachers are just average, and even exceptionally good or bad teachers can have their own exceptionalism overpowered by other factors.
This does not mean it would be wise or yield just-as-good or better results by throwing any person off the street into this role, which would be the natural implication of “it doesn’t matter which individuals you put in front of the classroom.”