Keeping your own guys into free agency isn't always the best move. We let Harper, Zimmermann and Desmond go, and instead were able to spend $90 million/year on 4 starting pitchers, and won the World Series.
We've done well letting guys go, but we also had a lot of internal replacements for big losses like Desmond & Harper. Not sure we have guys to replace Rendon & Strasburg but maybe FA and trades can carry us the next 2 years or so.
