First I wanna say that you make a fair point about a players bat only being "productive" enough to be considered good if he can play that premium defensive position. I agree with that idea, but where I disagree is saying these 2 fit that argument.
#1 Valaika - 2B is a notch down the defensive chart for more than one reason. His range coupled with his arm make him inadequate at SS (for my taste anyway) because even if he gets to some balls he won't likely be able to throw out the average runner as well. However his arm is no detriment at all at 2B so it kinda assists his range there. So in essence what I'm saying when I say his range doesn't play well at SS, Is that his other tools don't allow his range to be suitable. And his bat will play at 2B as is, if his discipline and power improve (which I have no doubt about his power improving) he's not Jeff Kent but could be a Ryne Sandberg (.285/.344/.452) level player or slightly better. What's not too like about that?
#2 Mesoraco - I agree he looked miserable behind the plate and that part of the equation has yet to be determined. But we all know it's by far the toughest defensive position on the field and it takes an inordinate amount of time to play it well. So a tad over a full year in pro ball doesn't give it adequate time to reach a logical ultimate conclusion in my mind. I'm also not sure we have seen enough to suggest his bat isn't capable of far better #'s than we have seen to this point. In fact if you take into consideration that he was perhaps hitting at a level higher than his age/experience would normally slot him then you might feel he more than held his own. I'm not so sure he was at a level higher but it's definitely arguable. So taking those things into consideration coupled with his talent and current position i'd say his value right now exceeds a guy who has exhibited for multiple seasons now that he cannot hit pitchers who throw from one whole side of the mound and that his talent apparently doesn't represent a future defensive gem himself (at a far less important defensive position).
Really i'm not arguing your rankings, we all have reasons for why we rank guys where we do and that's fine. But are we really giving these guys enough thought or are we just looking at the surface, forming an opinion and going with that?