I have done my absolute best to portray how damaging my ex's behavior is but he gives zero feedback during the process and he rarely wanted to hear it.
Most third-party professionals involved in my case wanted to know how I was focused on my son's well-being, what I was doing to problem solve under difficult conditions. It was never stated that way, exactly. My process involved a parenting coordinator and coparenting therapist, which may be different than what you are going through.
I do think the "game" involved is that they are looking more at your character and ability to be the emotional leader. If you disparage the ex, then they think that means you will behave that way with your child.
does the GAL's report and opinion trump the custody evaluator?
This probably depends on your L's strategy and how things work where you live. Has your L discussed with you what reports will be admitted in court?
In my case, everything we used to persuade the court all added up to the same narrative. It was documentation of the pattern of behaviors that mattered. If the CE report in your case is different than what your child's T and GAL suggest, then it may come down to how well your L does litigating in court. Not all lawyers are as good at this part of practicing law, some are better at pushing papers.