5G antennas are getting close to AESA (active electronically scanned array) radars used in military (X-band is 8 to 12 GHz). Unlike radars in fighters, 5G array can't cost millions per unit.
Someone with self-driving experience, please correct me.
Military radars are for detecting quiet targets, not cellphones wanting internet. It is total apples and oranges in terms of energy levels.
1. All you care about is getting the ratio of multipath energy high enough that you can resolve independent signals.
2. Remember RF power is measured in db and your radio's power consumption is in linear watts. 6db better signal margin means you use half the amount of energy. Useful for devices that run off batteries, have issues with heat dissipation.[1]
3. Less energy transmitted means your effective cell size gets smaller.
[1] Crusty old EE pointed out to me once the difference between a 85% efficient power supply and a 90% one is 65% less heat to get rid of. Same thing is true of RF power amps.