A) that more positions with higher average salaries have been created on a monthly basis than were eliminated since he
Preferably, "he" shouldn't refer to possessive "CEO's"
B) on a monthly basis that more positions with higher average salaries were created as had been eliminated since the CEO
meaning error; board of directors did not insist on a monthly basis, what the sentence really want to say is positions were created on a monthly basis. Also why would anyone use as? we need to emphasize that "more jobs were created than were eliminated" ı don't know how "as" caters to that intention
C) that more positions with higher average salaries every month were created than were eliminated since he
Preferably, "he" shouldn't refer to possessive "CEO's". Also "every month" is misplaced
D) that more positions with higher average salaries were created every month as eliminated since the CEO
we need to emphasize that "more jobs were created than were eliminated" ı am unsure how "as" caters to that intention
E) that more positions with higher average salaries were created on a monthly basis than were eliminated since the CEO
Correct