although I agree that this will promote economy and understanding, I also think that there will be some drawbacks.
Incorrect response. You are not being asked to give an opinion on the topic. You are asked to provide a general discussion regarding the advantages and disadvantages of English as the dominant world language. Provide one advantage and one disadvantage topic, completely avoiding any personal opinion since it is not required in the prompt. Do not alter the prompt discussion requirement. That will result in score deductions as your restatement + opinion paragraph is no longer related to the original presentation. Do not add information to this part for any reason.
several shreds of evidence
You are using this phrase out of context. Do not use English slang in reference to a formal and academic discussion. You must use an academic tone and avoid exaggerated references, such as this slang phrase. It does not have any place in academic writing.
millions of other linguistic teachers
Stop exaggerating. The examiners do not appreciate stretching the truth or over emphasizing information in the essays. This shows a lack of academic writing ability on the part of the student. The sense of logic in your writing disappears and the examiner is left with a piece of writing that lacks common sense discussion points.
Maintaining local languages and cultures should be prioritized to ensure a rich world heritage for future generations.
Another prompt deviation. You are 3 for 3 in terms of severe deductions for this writing. Add to that the lack of proper sentence formation in the conclusion, which is 3-5 sentences or 2 sentences of at least 40 words and you will understand why this is not going to get a high score during an actual setting. Most specially since you have a habit of adding unimportant or non prompt related discussion points in certain aspects of this essay.