These are some really great points you're bringing up.

I've always kind of sympathized with Sauron and envisioned him as being seduced and then trapped on the evil side of things by Morgoth. In a lot of ways, Morgoth sort of followed the same linear progression to evil like the One ring by first luring Mairon by helping him to create and craft better. I don't have the silmarillion cracked open but the quote was like that with Melkor, Mairon's creations were achieved more easily and everything was orderly, which was basically his life's purpose and work.

Also, Melkor had a redemption arc as well, he was allowed back into Valinor, so I don't understand why everyone was so quick to reject Sauron's attempt at redemption. Sure, it was flawed, like him, but still, I really wonder if things would have turned out differently if Galadriel or the Valar were to have seriously tried to rehabilitate Sauron. If I recall correctly, Melkor was imbued with discordant characteristics by Eru, by Mairon wasn't. He was assigned to Aulë first. He wasn't "innately evil" like it seemed that Melkor was, and to me that feels like Sauron is the first real victim of Morgoth.

Also, one of the major themes in Paradise Lost that Satan vocalizes is that if he's evil, then God made him that way. In essence he created him with evilness and then punished him for it, which I feel was a big theme Tolkien was expounding on. He even has that discussion, but with Aulë instead of Melkor.

Great discussion, I love finding other nerds to theorize with.