You are right. SAR is more complex than simple power density because of tissue resonance, penetration depths, and the non-linear way the body absorbs different frequencies.

My goal with this post wasn't to replace a high-fidelity 3D SAR simulation, but to provide a 'macro' comparison of the primary variables we can control: distance and transmit power.

Even when you account for the complex absorption profiles of brain tissue, the orders of magnitude difference in distance and power between a phone and an AP remains the dominant factor for total exposure.