I'm not sure I'm damaged as a player, but I was certainly annoyed.
His argument was that living things glow in astral space, so there is no way to hide from astral perception. And drones are everywhere, so my character had no reason to pay any attention to that particular drone until it shot me.
Basically, this GM turns the magic up to 11, so that non-Awakened characters are essentially useless.
Actually he's by the book correct, the issue is that it's just something you probably shouldn't do as a GM.
I will say that you might talk to your GM about effective measures for hiding from astral. Crowds are good. As are potted plants. A swarm of gnats or mosquitos will provide cover etc. Big public events like parades and rally's usually have a lot of background emotion that makes an astral perciever's job harder. Blending in emotionally (or being less agitated than the people around you) will help as well. There are ways to hide from astral perception, you need to find out which ones your GM allows.
Also, it's a rare security plan that depends on a mage patrolling astrally looking for physical threats. That's what guards, drones and watcher spirits are for. An Astral Mage is by themselves and exposed against astral threats, their body is empty and exposed and over a period of time it becomes uncomfortable. If your sniper is a key part of the plan (which he should be) see if the mage can keep a spirit (or a spirit and a watcher spirit so the watcher can run and tell him somethings wrong) hanging around astrally to play geek the mage with anyone who comes looking.
It's also worth pointing out that he would have to percieve you, return to his body or to an area with friendlies, manifest or return to meat space. communicate the information to someone who was controlling the drone, have the controller vector the drone to you, the drone would have to travel, pick you up with sensors, and then engage you. So it shouldn't be an instantaneous process.
At the very worst you should hae been able to have a chance to detect the drone incoming, and the drone should have had to detect you (probably with an opposed check against your sneak - possibly with a bonus if the mage took the time to give a detailed description of your hiding place) before it could fire at you.