Nagarythe/the Shaowlands is a desolate wasteland. There's nothing to plunder. The Druchii want the Asur out of it because a) it's the closest landing site to Naggaroth, and b)(far more importantly to the Druchii) it's Aenarion's kingdom, and they consider it their rightful property. The Shadow Warriors fight because they hate the Druchii more than anything else in the entire world. Like, yeah, they don't want the rest of Ulthuan to become like them. But they explicitly torture the Druchii out of hate and vengeance ("The hatred that the Shadow Warriors reserve for the Dark Elves is boundless, for the Sundering cost them not just their lands and loved ones, but also forever stained their reputation with suspicion and dread. Any Dark Elf captured by the Shadow Warriors can expect a long and painful death."). It's not a strategy to discourage the raids.
Desolate wasteland? Undoubtably, but now we are getting into the oldest argument the Druchii have, should Malekith become the Phoenix King? The issue that the raids and counter-raids brings up is that the population functionally had no difference in ethos outside of whether Malekith being rejected means to them.
The origin of the Shadow Warriors is explicitly stated as the survivors of the original settlers of Nagarythe who refused to join the rebellion against Ulthuan. They banded together and swore against Malekith and his ilk.
"
It is an unusual Elf indeed who has not heard of their valour. Though they are wilder and perhaps more vicious than the rest of our people, it is because of their tragic past rather than innate cruelty. Given the bitter times through which they have lived, this is a flaw that we find easy to understand." Pulled straight from wiki.
Finubar is stated as having sent a new Prince to Nagarythe who is explicitly stated as having made an alliance with the Shadow Warriors. It goes back to the fact that officially Ulthuan is not at war, the Shadow Warriors are remnants of a kingdom now constantly fought over between the Druchii and Asur, consistently behind enemy lines and always fighting. Honestly we could go around and around with the whole "one man's terrorist is another man's freedom fighter" because I would be willing to wager that some Druchii and possibly Malekith as well consider the Shadow Warriors traitors to them just as much as they do about the Druchii.
I think part of the argument is that we are outsiders looking into what amounts to a blood-feud inside of a family. Hatfield and McCoy style killing each other but within one family. If you will forgive a belabored analogy it's like watching two cousins going at each other with knives, the parents don't particularly care because they haven't been nicked by the fight yet. The family who care's have been hurt by one of the cousins so they root for him. Other's don't because the fight never reached them before dad made them go to separate corners.
Part of the issue with this entire argument is that it is entirely in reference to high minded politics and huge issues between the two cousin races ignores the reality on the ground.
An Averlornian weaver who has never suffered a Druchii raid isn't going to care.
A Cothique fisherman who lost his brother to the Druchii will hear about it and cheer.
The Saphery High mage is going to consider it ancient history as she studies the spells that were used to rip cities apart. She will look upon it as if they are stupid children fighting over dust.
The Tiranocian noble who's sister died on Druchii pikes during the Sundering is going to donate more supplies to the fight.
It isn't about reality or strategy, it's revenge, plain and simple. A population who suffered and was told to simply get back to work and told "There is no war in Ba-Sing-Se/Ulthuan" isn't going to simply forget, they are going to cheer on the people who refused to come in from the cold. Who looked back at the Phoenix King and said "We remained loyal, the fight isn't done until we've won too."
