So your saying that Eaton is going to maintain or even improve on his current numbers that he has posted this year already, and be much better than what he was last year?and that Santana will get worse or stay the same from what he has posted already this year, and be much worse than what he posted last year?
Pitchers don't always perform the way they did the previous season, especially young pitchers. There tends to be a lot of variation.
Eaton is in a new pitcher's park, and he's pitched exceptionally well this year. Santana has struggled somewhat (5 HR allowed in 35 IP).
Personally, I don't think the difference between Santana and Eaton (or between Rhodes and Julio, for that matter) is that great. The trade looks like a lateral move, IMO.