Where Ethan's concerned, I'm wondering is that they both wanted an early winner (since Hatch and Tina were axed before filming), and as you said, he had a good story. I do think Ethan, like most old schoolers, couldn't keep up with the pace and the now of the game. It seemed he was more on relationships and alliances being solid than anything else. Parvati said she only kept Adam because he and Ethan were friends, but that voting Natalie out probably hurt her game. It likely hurt Ethan's.
I don't know that I'd be opposed to some winners returning from this season, but Sandra, Parvati, Boston Rob, and Tony definitely don't need to return. Tony got really lucky this season. The fact that he was the 2nd boot during Game Changers shows what will happen if luck isn't on his side next time. And I wouldn't be opposed to seeing Amber again, but she likely would have a rough go of it even without Rob around, just for being married to the guy. I actually wouldn't mind seeing Nick, Sarah, or Adam again. And I'd love to see Yul, although I don't think he'd do it again. I don't know if there's anyone else, though. I personally don't care to see Tyson, Jeremy, Kim, Denise, or Ben again. I don't know about Natalie, my feelings for her changed a little based on some of the post-show stuff.