Yeah the maximum npc difficulty should equal 100% chance of death if big error against them, even for veterans, even in small/medium groups. It is balanced that way now and offer a real challenge.
Lets wait for heavier chassis ingame to see even more challenging pve. Because i think the game misses something in the area of "biggest threat possible". Maybe change the way pve HL is handled, why not use POS as an opportunity to do this?
Once we have our new islands adapted for structures creation, why not make the faction npc build highly defended structures, at random locations, preceded by roaming activity etc... What is most fun and realism, a giant robot/monster/whatever with 1 billion HP, that take a 40 players group 1hr to kill, or a giant fortress defended by swarms of low npcs, defensive turret structures, and maybe some observers or a little stronger opponents at the center near the loot.
From a lore/evolution of game perspective, i think implementing npc actions inside the POS system will be essential to develop the "war against natives" aspect of the persistent world. Once we get further inside Nian empire, we will obviously encounter ennemy structures. I think those structures should be almost all destuctible, except some key buildings. After that its easy to regularly adjust aliens response level to be in line with the story.