I think currently the Grasshopper-ARCHICAD Connection does not transfer element geometry resulting from Priority Based Connections, such as the stepped Wall skins at corners or stepped skins resulting from an intersection of a Wall and a Slab.
These are transferred to Grasshopper as extrusions as far as I can see. I guess the feature just has not been fully developed yet. However, cuts resulting from Solid Element Operations and Trimming to Roofs/Shells do get transferred, so we are getting there.
That being said, I fully support you request.
By the way, I just found that yes, the BREP is triangulated for some reason. I don't know if it is a Grasshopper thing or a GH-AC Connection thing. However, I found you can solve this by connecting the "BREP" or any of the "Surface" outputs of ARCHICAD Deconstruct Nodes into a Grasshopper "Mesh" Node, and it will result in a non-triangulated Mesh Surface. Please note that if the Grasshopper-ARCHICAD Connection is installed, Grasshopper will have 3 Mesh Nodes. You will need the native Grasshopper Mesh Node for this.
Or, you could use the "Mesh Brep" Node, which will approximate a BREP with a Mesh geometry, and you can define several parameters for this approximation.
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