Dropping an RKG-3 grenade on a tank from a cheap drone also requires that the tank be stopped -- something that happens far less often in a war of movement than in trench warfare. The war in Ukraine has been extraordinarily static (like the Nagorno-Karabakh War), and this has provided the opportunities for COTS drones to be useful in this way. A combined-arms offensive on a divisional or corps front might take a handful of losses this way, but it most certainly will not be stopped.