Do not put this person's name on the patent as an inventor! And please do not treat their advice as gospel.
First, they are breaking the rules by providing advice to you about your filing. It is practicing law without a license. Next, the examiner is correct that all inventors need to qualify as micro entity applicants.
From the form
GROSS INCOME LIMIT ...
Double patenting results when the right to exclude granted by a first patent is unjustly extended by the grant of a later issued patent or patents.The doctrine of double patenting has been created to prevent the unjustified extension of patent exclusivity beyond the term of a patent.
The following criteria are considered for the issue of double patenting, ...
The patent office will only communicate with one party. In this case it would be the attorney/agent with the power of attorney. In the case of multiple inventors they can designate one if them to speak for all. I’m sure you can see the reason they need to only deal with a single party.
There was a famous case regarding putting an eraser at the end of a pencil. It was granted a patent by the USPTO but disallowed by the Supreme Court in the 1800's. The eraser didn't do anything different becasue it was attached to a pencil and the pencil didn't do anything different becasue it was attached to an eraser.
We do not use the term synergy in ...
It isn’t moot - it would be positively improper to add them. In the U.S. an inventor is someone who makes a conceptual contribution to something in a claim. Someone might be an inventor in a divisional but not the parent application, for example, if the they contributed conceptually to something claimed in the divisional, not the parent.