You'd trade Castro and Baez for Harper and add another top prospect? I'd at least think about it, because prospects bust. If you promised Baez + ________ (Soler or Almora) would both come close to their peaks, then no I wouldn't do the trade. However, since they are still in the low minors it isn't out of the question. Harper put up a 5 WAR at 19, he's going to be the best player in baseball or at least one of the two best. I'm higher on peak age Harper than peak age Trout, personally. ETA: Castro+Baez+Almora/Soler for Harper would still be a bad trade for the Cubs, but it's not an immediate no. Why would a bad trade for the Cubs not be an immediate no?