as you said, I find also that “brute force” approach is not a solution, especially if there are hundreds of different parts.
I have spent some time searching for similar topics and plugins but I was not able to find any functional solution. For example script here works well but it still can not distinguish mirrored Breps:
It had surprised me that until now there is no some plugin free/or with subscription that tackles this topic, considering that work of many Rhino users is related to production ready modeling.
Nevertheless I was able to make some halfway solution where I am comparing distances between breps centroid and the breps faces. The only thing is that if in the model there are some mirrored breps, that script does not recognize as different parts. Insted it groups them in the same branch as original breps
For that reason I am trying to get the breps stacked on each other and make a second check in order to identify those mirrored ones