The Most Average
Now that we've looked at the best and worst average seasons that Pirates pitchers have had, what are the most average, based on all factors? 2011 Paul Maholm takes the title for the starting pitchers. Maholm had a 3.66 ERA and 3.78 FIP, giving him a 99 ERA-, 100 ERA+, and 101 FIP-. On top of that, Maholm had a 2.0 fWAR, on the dot. You could also argue Sisk's '67 season, though, with a slightly higher fWAR, I decided to honor Maholm here.
D.J. Carrasco's 2010 season is named for the relief pitchers. Carrasco has the closest ERA- and FIP- to 100. He clocks in at 99 and 97, respectfully. During the '10 season, Carrasco owned a 3.88 ERA and 3.80 FIP while pitching for the Pirates. But he was traded at the 2010 trade deadline.
If you want a reliever who spent the entire season with the Pirates, then 1963 Roy Face gets a second mention. He had a 99 ERA- and 104 FIP-. Carrasco was within 3% of the average FIP, though Face was only within 4%. That slightly 1% is why Carrasco was mentioned, though since he didn't spend the entire season in Pittsburgh, you could give it to Face here.