I won't go into whether the isle was good or bad, but you are way underestimating the impact of it on the game. There's a reason why rob constantly mentioned how it was a PITA in trying to manage things.
Outside of perceived threat that Rob felt, at no point did the returning castaway have any impact on the game. They didn't get anyone else voted out, and they were not in the final three. It was a true waste of time (listening to Matt praise his god for fucking him over was beyond boring).
Using my rules above, there is no way anyone is throwing a challenge to get Russell out, else he could wind up on the opposing tribe and be even more of a post-merge threat.
Ultimately I just don't like the idea of giving a second chance, but I do understand the need to mix things up to keep the game fresh.