Not to forget mentioning, my inadequate English language skills does not make the fact less of a fact that you are not qualified to write papers in other academic disciplines.
Nice try at changing the subject. You are correct that your lack of English skills has nothing to do with my capabilities. You are incorrect that I am unqualified to write in "other academic disciplines" (other than what?).
You degrees are not enough to make you write perfectly on topics which do not require perfect English but analysis and core concepts of the subject.
All academic assignments "require" academic-level English. I agree that my degrees alone do not qualify me as a writer in other disciplines, but I have taken classes in many other disciplines and have proven my qualifications in many areas through years of work in the industry, as well.
More often than not, I write for ESL students who have no issues with me being an ESL writer, because they themselves are not proficient at English language
Good. It should be "always," but this is a start.