One simply needs to visit any Chinese university and sit down with a few random members of the graduating class of English majors.

They cannot speak English.

Perhaps twenty percent of the class can hold a conversation. Perhaps five percent of the class speak well.

Bringing thousands of foreign 'teachers' to China to 'teach' English during the past two decades has been a marvelous business venture but an educational fiasco.

What you don't know is how woeful the statistics would be without native speakers of English teaching such students. However, what we can say, generally speaking, is that non-native speakers of English, such as Turnoi, are no better than the Chinese teachers of English as far as the teaching of oral English is concerned. I disagree with your assessment of the effect of bringing foreign "teachers" to China being an educational fiasco! What you don't know and didn't mention is the positive influence of oral teaching by FTs at high schools on pupils who later enter higher education as non-English majors. Some such students can speak better English than English majors!