Do you believe that Rizzo and Castro are "core" players going forward ? Can you answer that ?
Even though both players are far below the league average.
Rizzo is not below league average.
OPS+ is 105, wRC+ is 104. On both of those metrics 100 should be roughly league average. By fWAR he ranks 14th among first baseman, right in the middle the pack for MLB at that position.