Or they could just use a non-harmless power and focus it on large on-ground receiver stations. Could use some security on the satellites like interrupting automatically the beam on sensing an unpredicted movement (up to when a "continue" greenlight message is received, after needed corrective steps).

Other possibility is to use stratospheric balloons as receiver stations. Could then use softer power links to the ground. Would some system of cables be doable then?

(I wrote that in the optics of a Dyson's sphere [thus connecting space solar stations to an on-ground power grid] instead of the proposed direct powering of drones.)

At those intensities, microwaves seem significantly less useful than optical PV.

Microwave rectenna is more efficient than optical PV. Also, microwave is less affected by weather than visible light. As a power source, they also can have much higher capacity factor than PV.

Well, they work at night if your solar power satellite is high enough (eq. GEO).

The same applies if the beaming is done with an optical laser instead of a microwave.

Optical laser is rather inefficient at converting electricity into optical energy. Surely there are some low-powered diodes where one can get over 50%, but for powerful lasers efficiency like 1% is a good number. Consumer microwave ovens on the other hand has efficiency like 65%.

Sure, that's true - I guess microwaves still could have some benefits, for attenuation in the atmosphere/weather maybe ?