The un-weakened fortresses (owners not assassinated first) were easier than many outposts IMO, Min's was a bit harder, because you have to fly over and crash-land on the cliff behind undetected, but once you killed the roof guys with suppressed sniper fire for the long shots, and the crossbow up close, you have easy access to a mortar, stationary HMG, and even an RPG in case the cavalry get called in.
I'm gonna do the hard difficulty next too, but I still have to complete story missions (I haven't even done the attack faux-Min yet), Y + R Shangri-La and whatnot. Pretty sure I got all the Longinus. I also want to try out the rest of the locked superguns, the wire-guided rocket launcher &ct.
EDITED: 17 Jan 2019 14:23 by DSMITHHFX