Here’s my thought: TunkRank assumes in its model that, if X reads a tweet from Y, then there’s a constant probability p that X will retweet it. If this assumption holds true, then the TunkRank of X should be roughly proportional to the retweet rank.
Of course, one of the reasons this assumption might fail is that X is using bots (or bot-like people) to game his or her retweet rank. It’s also possible that the TunkRank assumption about a constant probability of retweeting is too simplistic.
But I’m intrigued at the idea that, subject to the assumptions of its model, TunkRank acts as a sort of ungameable retweet rank.