>>36714570To me, it comes down to this.
To be a coomer, one only needs to make a habit of engaging in sexual activities (porn, masturbation, etc) periodically. Enough so to a point where it's a normal part of life.
To be a coombrain, one needs to be so obsessed with engaging in said sexual activities that it dominates the vast majority of their time. Thus the brain itself is coom incarnate.