The broader picture is that, after two-thirds of the season, the starters' ERA is about 4.50. Looking at individual pitchers, as some have tailed off, others have picked up the slack. As has been noted, NL teams may have figured out Nova. In his first 11 starts, his ERA was 2.92 and batters hit .259 against him. In his last 11 starts, the ERA is 4.52 and the BA is .284.
But both Kuhl and Williams have improved. Kuhl's initial 11 starts featured a 6.02 ERA and .293 BA against. In his more recent 11, the ERA is 3.30, with a .251 batting average. Williams was also shaky at first. His first 8 starts include a 5.09 ERA, but the past 8 harbor a 3.69 ERA.
Cole is, for all the scrutiny on him, very steady by contrast. The BA against him in starts 1-11 was .256. It's been .259 in the latter 11. The number of walks allowed, however, rose from 14 in that first eleven to 19 in the second eleven in nearly the exact number of innings pitched in both sets.