A good method is to find a Base with a hill on one side, where you can hide from their field of view and do a hit-and-run on the Banshee until it'd destroyed.
Then use the same tactics for the Revenants. I used Premium synth on Scorpion missile launcher and it allows for 1-shotting the drones. If you do that their friends don't get aggro, so you can 1-shot them one by one, then do a quick scoop run, and then hide at the bottom of the hill and wait for a Scout to drop a new batch of Revenants.
Also, you get 3 mats for 1 collected, so it's fairly easy to get loads of them.
Audio is in Polish, but you can see all of the above here (link is timestamped):
Source: https://www.twitch.tv/videos/2125079637?t=03h42m58s
I call it "The Clooney Method"