as far as him having an "unquenchable thirst" for revenge on Thor. I think that is really putting him back into the pure evil 1 dimensional villain box again, and I really don't think they want to do that with him. A good chunk of the audience have become emotionally invested in that character, and would be pretty upset if he just became a completely evil bad guy with no humanity left. They also want to keep these characters relatable, and pure evil is not very relatable.
But it's really not putting him as a one dimension villain though. Yeah, it's a one dimension aspect, but it's rooted in deeper parts to his character. And it's essential to his character. Again, it's a one dimension thing, but it is rooted in something much deeper. He can certainly have a desire to get back at thor, or cause him pain, or be superior, and still have complex reasons to do so. Regarding your perspective on this, I really don't think loki's opinions on thor are that much of an issue, cause it does go pretty deep. You can have a one dimension aspect without being a one dimension villain. Again, as I said, Thanos wanted to destroy all life, a one dimension aspect, sure. But he certainly isn't a one dimensional villain.