Even though the new CEO’s critics complained about the rate at which e

IMO E

A) that more positions with higher average salaries have been created on a monthly basis than were eliminated since he -> does not have an antecedent

B) on a monthly basis that more positions with higher average salaries were created as had been eliminated since the CEO -> meaning error

C) that more positions with higher average salaries every month were created than were eliminated since he -> does not have an antecedent

D) that more positions with higher average salaries were created every month as eliminated since the CEO -> wrong use of as

E) that more positions with higher average salaries were created on a monthly basis than were eliminated since the CEO
Correct

Even though the new CEO’s critics complained about the rate at which employees had been fired under his management, the board of directors insisted that more positions with higher average salaries were created on a monthly basis than were eliminated since he took up the position.

A) that more positions with higher average salaries have been created on a monthly basis than were eliminated since he -> I see multiple errors, 1) x have been....than were.. It is glaring parallelism error. 2) he (non-possessive pronoun) cannot refer to the new CEO’s (possessive pronoun). Incorrect.

B) on a monthly basis that more positions with higher average salaries were created as had been eliminated since the CEO -> higher....than...is correct form. We shouldn't use "as". Incorrect.

C) that more positions with higher average salaries every month were created than were eliminated since he -> There are multiple errors again; 1) Did higher average salaries every month create or Did higher average salaries create every month, 2) he (non-possessive pronoun) cannot refer to the new CEO’s (possessive pronoun). Incorrect.

D) that more positions with higher average salaries were created every month as eliminated since the CEO -> higher....than...is correct form. We shouldn't use "as". Incorrect.

E) that more positions with higher average salaries were created on a monthly basis than were eliminated since the CEO -> This is better. We can see, higher....than..is correct form. Pronoun is replaced with Noun (the CEO), it makes sense.

So, I think E.

Correct Option E

Even though the new CEO’s critics complained about the rate at which employees had been fired under his management, the board of directors insisted that
more positions with higher average salaries were created
on a monthly basis
than were eliminated since he took up the position.

Eliminate B: Correct Idiom : "Insisted that"
B) on a monthly basis that more positions with higher average salaries were created as had been eliminated since the CEO

Eliminate C: Pronoun "he" creates ambiguity, and sentence structure error, avg salaries are compared with elimination of job.
C) that more positions with higher average salaries every month were created than were eliminated since he

Eliminate A, Tense Error "have been" and Pronoun ambiguity "he"
A) that more positions with higher average salaries have been created on a monthly basis than were eliminated since he

Eliminate D, comparison error, rather than "more X than Y" is correct Idiom needed
D) that more positions with higher average salaries were created every month as eliminated since the CEO

E) that more positions with higher average salaries
were created on a monthly basis
than were eliminated since the CEO
Correct:
1. Correct comparison error: more X than Y
2. Parallelsim maintained "were created" to "were eliminated"