a bit peculiar to me that anyone calling themselves a rationalist would believe that the brain is primary to the mind
Your perplexity perplexes me. Please elaborate.
Do you think the senses are some conduit from the world outside our mind into the world inside our mind?
As in, if you look at something, you are getting a somewhat faithful representation of the thing you are looking at?
For example, do you think your thumb is a part of fundamental reality?
In the source code for reality, is "polymathwannabe" or polymathwannabe's thumb?
I don't think so.
The source code just has a huge array of particles. The thumb is something a mind projects onto those particles. So is the brain.
A rationalist should be aware that their senses don't reveal reality to them, their rationality does by inventing theories based on stimuli.
I did a search about property dualism and I couldn't see much written here on this site.