I don't have any experience with the AWA grading scale but I can point out some grammatical issues:
"The presented argument is flawed because of the assumptions it made without providing proper reasoning"
assumptions it made is passive voice and somewhat awkward.
Try; The presented argument is flawed because it
makes assumptions but does not provide proper reasoning.
Another thing is that you start many sentences with "Argument xyz" this needs to be "The argument" as you are not talking about the broad concept of argumentation you are talking about a specific argument.
Also I would try and find ways to re-state ideas using new terms rather than using and re-using the same phrases, even if they are taken directly from the passage.
Ex: "who responded showed their interest only in topics of corporate restructuring and redesign of benefits" few sentences later "in the survey showed their interest only in topics of corporate restructuring and redesign of benefits"
For the second time around try and maybe say something like "showed interest in the benefit of changes to corporate design and structure."
When you are reading a few short paragraphs like your response it really sticks out when your eyes roll over identical phrases and words. I also believe the grading algorithm looks for this as well and as varied as your word choice and sentence structure can be the better.
Lastly in further attempt to get more words in and vary your word choice perhaps give some examples/reflect a little more on your points. For example after discussing why the 1200 respondents may not be representative of all workers you could say, "We do not know whether these survey respondents were all readers of a business publication and more likely to be interested in corporate issues, or if they were somehow randomly selected from the working population by the researchers. As a result it is not possible to judge the survey results as representative of workers in general"
By doing this you can take some time and just let some sentences flow out and not have to worry about thinking through any new points to you argument. Just take that one point and develop it out over a few sentences.