Without trying to trot out my CV, I'll say that my academic performance was never reflected by the scores on standardized tests. I also note many students of mine over the years who excelled and demonstrated brilliance in certain performative milieus but who, for a variety of reasons, could not perform on a closed-ended, multiple choice, timed standardized test. What have your years in the classroom revealed about student ability as reflected by external assessment?
My years in the classroom suggest you are full of shit.
"Many" students do not have trouble both performing on standardized test as well as other performance measurements. Perhaps a few, but I cannot think of "Many."
However, "Many" students that cannot, or have not learned standard skills and knowledge cannot do well on standardized tests.
Teachers who have trouble admitting this obvious fact are normally the deadbeats who do not like teaching to standardized methods, do not like composing assessments, are too fucking lazy to grade frequently, and like teaching so they are never held accountable for their poor performance.