It was all good until now, but I had to lower the difficulty to be able to kill flycatcher's drone. That thing is so fast I couldn't even react to it before getting killed by its gun. But I put it back on extreme right after. On easy the AI has amnesia, they go back to regular patrol in like 5 seconds after loosing you.
I've kept it on medium. I briefly tried easy to see the difference and it was as if all the Sentinel soldiers arrived to the island on a short yellow bus.