Ok, it's not an unreasonable way to look at it.
I guess I look at it as more of Ellsbury is here for this season, and highly unlikely to re-sign in Boston(Boras will be asking for a Crawford deal, I have absolutely no doubts) and getting back a young SP that has mid to upper rotation potential for at least 2 seasons is about the best I think we could expect for one year of Ellsbury with his inconsistent history.