So I did some looking at the actual numbers....

There's been 58 pitchers who are in the Hall of Fame who pitched at least some in the 1903 and forward era.

Of those 58- first off- 5 guys never played in the playoffs. Rube Waddell, Jack Chesboro, Jim Bunning, Fergie Jenkins, and Ted Lyons.

17 guys pitched to a higher ERA in the postseason than they did the regular season. Of these 17, only 2 had a postseason ERA more than 55% of their regular season ERA. Hal Newhouser and Gaylord Perry.

What I think is a really interesting number is 12/53 HOF pitchers have their postseason ERA +/- 5% of their regular season ERA. 25/53 guys within 20% of their regular season ERA.

So Kershaw is a really an extreme outlier I think. By far the most extreme guy in the last 30 years. I mean, no other HOF guy in those 30 years that is over the 20% mark either way. Before this- it's been Pedro at 18.1% worse and Smoltz at 19.8% better. This years HOF class could change that- as 5 of the top 6 pitchers by the BR hof meter are outside that 20% threshold-
Wagner 77% worse
Santana 24.1% worse
Hoffman 20.6% worse
Clemens 20.2% worse
Schilling 35.5% better
(kershaw for the record is 88.3% worse right now)