Having tall 1Bs has more to do with the classic profile of a power player at the corner, rather than any defensive necessity. Teams want power players at 1B, power players tend to be bigger guys, etc., etc. As a counterexample, Allen Craig is 6-2. Do you think his 3 inches on Dayan really means anything defensively? Probably not.
Personally, I don't care where Dayan plays. He needs to hit better, or he won't be worth much either way.