I have spoken English all my life. I have read millions of words
of English in thousands of books, newspapers, and magazines. I
have studied English for years, especially the grammar of English.
When I say that a word group is not English, I mean that I have never
heard that word group used that way, that I have never seen it used
that way in writing, that I never use it that way, and that people who
are competent native speakers of English do not generate those word
groups. Not being English means being ungrammatical.
To repeat:
Sentences of the form
Who that has a good idea should mention it at our next meeting are not English. Correct, grammatical English requires
He who has a good idea ... or, even more usual,
Whoever has a good idea ...
You are free to persist in holding a different opinion, of course, but
I, too, would request your criteria and your justification.
CJ