As far as I can see, based on a very quick skim reading, the study is essentially divided into a consideration of impacts from fundamental and spurious emission

As far as I can see, based on a very quick skim reading, the study is essentially divided into a consideration of impacts from fundamental and spurious emissions from 5G transmissions. For the fundamental emissions, the study considers primarily the impact of receiver front-end overload on the operational margins for the radar altimeters. The referenced ITU document suggests that radar altimeters are specified with "modest selectivity", e.g. 24dB/octave below 4.2GHz up to a maximum of 40dB. I believe that a power spectral density envelope derived from the ITU specifications is the basis of the fundamental emission calculation, not assuming the entire power will be dissipated spuriously. This is nowhere near my area of expertise, but it seems like those selectivity assumptions (I have no basis for opinion about them) in conjunction with large gains from beamforming are what creates the perception of risk.