In my office, I have a mini legal library- books to help you look at your situation, see what self-help options exist and then you decide whether to use an expert or do it yourself.
You can always have an expert come to the mediation session so that both of you hear the same info at the same time.
Often, people simply do not have the basic knowledge to do this on their own and it can quickly get complicated.
Your mediator will help you have the discussion about it, will likely have more information than you have, but they are not a “retirement expert.”
This area is simply too important to let feelings get in the way. I have heard people say that they are just walking away from retirement because they want to be done with their ex. While I understand the emotions, I also caution you. In a few years, that money you gave up might come in handy. When you realize their pension was worth over a million dollars and you might not be able to retire… my guess is that you will have second thoughts and not be able to do anything about it.