Mirrors are not effective enough. Shielding drones from energy weapons seems like a similar problem to entering Earth’s atmosphere, you want to shield it in a way that will blast away safely and ideally diffuse the laser, so the energy is spread over a larger space. I suspect larger lasers will likely aways win, since there is only so much shielding can do. At which point we could end up with transformers like drones that are built to be broken apart mid flight and yet still deliver damage. I feel like defending drones could become possible with energy weapons but only under ideal weather conditions.