I haven't read the LNs, and have no opinion on whether it's Haruhi's mind or Kyon's. Either way, after watching it, I was left with a feeling of emptiness and

I haven't read the LNs, and have no opinion on whether it's Haruhi's mind or Kyon's. Either way, after watching it, I was left with a feeling of emptiness and the sense that life is meaningless if you're not able to interact with other minds that are independent of your own but can still understand you. If the world is wholly a product of your own mind, and there is no objective reality, you had better delude yourself in to believing that the other minds that populate it are independent. Otherwise you'll constantly be destroying and recreating the would in search of novelty because you've given up on meaning. The best way to convince yourself the world is real is if the other beings in it know things you don't know and can do things you can't do.