Since 4/7, the Nats have gone through the rotation 4 times. the numbers:
Gray: 22.2 IP, 8.34 K/9, 3.73 BB/9, ERA 1.59, FIP 3.69
Gore: 22.1 IP, 12.05 K/9, 4.98 BB/9, ERA 3.32, FIP 3.57
Williams: 21.1 IP, 5.91 K/9, 2.11 BB/9, ERA 3.80, FIP 4.13
Corbin: 22.1 IP, 6.04 K/9, 2.42 BB/9, ERA 4.84, FIP 5.17
Kuhl: 17.0 IP, 7.41 K/9, 7.94 BB/9, ERA 10.06, FIP 7.62
Gray - helped by suppressing homers a lot and a ridiculously high strand rate of 89.8%
Gore -cut the BBs. High HR/FB rate hasn't hurt so much because he's 50% GBs.
Williams - low walk rate has helped.
Corbin - Basic difference between him and Williams is HR/FB. Williams is 7.1%, Corbin 16.7%. Corbin throws more GBs and gets more pop ups, they are hit roughly the same in terms of direction. Launch angle and hard hit% per Statcast suggests Corbin is more often harder hit and a lower launch angle (10.6% vs. 14.8%).
Kuhl? Not much to say positive about the on-field performance so far.