alternatively, mark them as detail
This doesn't really work. BSPC still treats them as brushes. Most of oacmpctf3 is detail yet BSPC kept throwing the dreaded "ERROR: Tried parent". Only when I turned those things as models (with the respective adecquate settings) did the map compile well.
Not to mention that the map was already clipped/botclipped/botdonotentered.
I wonder if it's the fact that such brushes weren't caulked or there were many complex brushes interfering. I had to properly recreate most of those objects while leaving the old geometry as weapclip brushes.