If you don't think The Lich King is literally the best developed Warcraft villain Blizzard's ever had, then you pretty much hate every other villain Blizzard's written because no one has had as much development as Arthas.
You can use that overgeneralization analysis with any villain, really. Doesn't mean they aren't well-written, it just means you lack fundamental skills to critique beyond "everyone's like the devil, was good, something happened, became bad lulz, next."
Arthas is very different from Neltharion, see above.
Archimonde has always been viewed, even in lore, as an arrogant, and poor strategist, even by Kil'jaeden himself. It's why I find laughable he could beat LK and the entire Scourge.
Questionable whether Alextrasza, Ysera, or Nozdormu could just beat Arthas as LK if they wanted, why didn't they, then? They were right there in Northrend helping the war cause. Deathwing for sure after he was pumped full of N'zoth steroids.