I appreciate that in your brief analysis you are considering several mechanisms of action besides just the heating. There may be many kinds of resonances, at molecular level, supra-molecular, etc. If very little 900/1800MHz suffices to alter BBB, then it is like a trigger to worse things, without the need of much energy. In the animals tested, the amount reaching the brain, at typical GSM levels, had already the observed result. Of course my tone is speculative here, but if the effect was confirmed in humans, it would not need much energy, and just the medium-to-weak signal reaching the brain could be worrisome.
There are not yet any studies on it, but if the effects of 5G on BBB were much stronger than with 900/1800MHz, it may also be the case that much lower signal intensities would still alter noticeably the BBB, even after the attenuation of the body traversal.
I am not a luddite at all, but I do hope that scientists working to certify that 5G is healthy are not hand-waving away the problem only by saying that the energy absorbed is too low or that the body is blocking its intensity. That would mean they did not hear at all about the effect of the mere frequency as a signal on the adhesion between cells.
I really would like to see some study elucidate the mechanism (or the absence thereof, and the flaws of the previous study), maybe some sort of resonance, soon enough to avoid to be in a situation were Wifi/4G/5G would be everywhere yet with dangerous long-term effects on health.
I'd worry more about standard heat given off by devices like laptops. The radio emissions aren't gonna do much but the 80C hot air out of the exhaust blowing into your lap is definitely going to do something. There is plenty of studies on the effects of overheating genitals in males.
But back to the topic; the energy is too small. If these radio waves had an effect, being out during a cloudy day would. The energy you get from solar radiation over a day is probably about the same.
Things like DNA breaking apart don't generally happen with this low frequency, largely because they require a bunch of energy to happen. Like ionization, even 1000W of 100MHz radio waves aren't going to make it happen. There is no amount of energy you can dump into a 100MHz transceiver that would cause ionization of atoms. It simply won't happen. Well, they will ionize but not because of the radio waves but because they've heated up enough that they're starting to undergo plasma formation. But that semantic difference is still important.
The sender in your cellphone or the energy you get from your wifi router are too small to be measured and by all acounts of physics, their effects are too small to be reasonably measured even in long term studies. We're talking literaly sub-milliwatt over your entire body. The entire body uses atleast 100Watts to stay alive. <0.1% change in thermal energy.
However, I really hope they find what was the flaw(s) that led to the surprising result on the BBB of rodents.
Blocking signals with your body becomes more true as frequency (and bandwidth) goes up. 5G Wifi can't even properly penetrate dry wall, not even mentioning all that water and bone in your body.
Beside that, below the infrared spectrum, it is unlikely that much damage is done by common RF signals; the energy in a quanta from that spectrum is too small to effectively do anything but heat molecules up a tiny bit.
Photochemical effects, ie, things like chemical reactions being induced or cells reacting to the light, require atleast about 1Thz to work (low-end IR).
The heating occurs primarly for frequencies between 30 and 120MHz, which is actively used but not by B2C commercial things, it largely involves ham radio, air traffic radio, sea traffic, weather satellites, etc. Things you're likely to be closer to the receiving end of than the high powered sender.
Which also bring to the other issue; the energies in common RF close to you is too low. If you send with 100mW power, the power your body will capture, even if it's the phone right next to your ear, is likely below 10mW of power. Low enough that your native body heat already overpowers it easily.