(Copying from a facebook post I made, so some of you may have seen this already.)
Teela, while hurt by those she loved, grew up knowing she was loved. Lyn grew up knowing she was just a resource to be used, never really knowing love in either direction. Even when rewarded, it was only to help her become a more useful resource.
Teela's relationship with Adam/He-Man may have been flawed due to the lie between them, but it was a flaw in a good thing. Lyn's relationship with Skeletor was at best satisfaction of mutual craving. Her first positive relationship was during the first part of the season, where at least everyone was honest about not trusting her, and they were starting to move towards friendship.
Each took their own pasts into views of the cosmos. Teela saw beauty hidden behind secrets and lies, and wanted to bring that beauty to everyone. Lyn saw chaos and pain and inchoate darkness, and felt that the highest good she could do with power is to burn it all down.
Both saw the world they were raised in as flawed, broken. The one who had known love fought to fix the flaws, even if she had to oppose those she loved to do it. The one who had not known love saw no solution save annihilation.
---Dave