"In audio morse there's a plateau at about 12 words per minute [...]"
Many years ago one of our radio club members related an experience during the war. He had hit a wall with the next morse receiving speed grade required by his job. Finally his boss sat him down with a pad - and a packet of 20 cigarettes. He was not going to be allowed to stop until he could read the boss's morse at the required speed - or he had finished the cigarettes. He managed to reach the grade - but not sure how many cigarettes were left afterwards.
I suspect most learners can send morse faster than they can read it. I passed my morse test on the second attempt - but the testing officer in Liverpoool was definitely being kind to me. Never really used it in anger - so never acquired any real competence. Some 50 years after not renewing my licence my fingers can still tap out CQ de G3T** ar k