My interpretation of Garza's WAR is that replacement level pitching is always worse than we think it is.
In 2017, it looks like replacement level xFIP was around 5.4. So closer to 2017 Junior Guerra, who started 14 games and racked up -0.1 bWAR, -0.7 fWAR. So as bad as Garza was, the 2017 Brewers still had to cover about 25 starts with guys who were worse than him.