I get where ATF is coming from in that there were some rather surprising performances (ie. Grossman, Baddoo, maybe even Candy to an extent) that may not necessarily be replicated next year.
On the other hand, they aren't gonna be trotting out Willi Castro and Niko Goodrum at short stop and adding the two youngsters, even if they are green, are gonna be net additions to the existing lineup. Maybe upwards of 3 WAR
As for how they grade out, I don't think they are gonna be the worst lineup in the American League... that's probably gonna be Oakland and Baltimore. I do think they are still in the lower half though, depending on how the youngsters progress