WAR can be deducted as well. Just because X player has earned it to date doesn't mean they can't drop below that number.
We cannot realistically expect Ezequiel Carrera to be a 10 WAR player / 600 AB's (a full season). He has a BABIP of .500 which is impossible to sustain at the ML level. Coupled with the fact he barely walks and is striking out above league average rates, it's easy to see why he will regress.
Although not perfect, Navarro loses a lot of his WAR value from framing, which is not incorporated into the WAR number. He's basically a league average bat on the bench, with very little positional value. He's basically a $5M pinch hitter.
Santiago was worth 2 WAR five years ago. It's safe to say his best days are behind him.