[Cynical]

1989 explains a lot; I've read elsewhere that older leagues are coded to have pitchers show less fatigue, mirroring how everyone went a lot longer in those days. In 2020, IME, if your starter threw 100 pitches, even on four days rest he'll still be "slightly tired" when his next turn comes up.

EDIT -- I'm curious, how do your starters look after three days rest? In the late '80s, and even as far as the mid '90s, there were still a lot of teams running four-man rotations, and I'm wondering if your guys would be "fully rested" or "slightly tired" generally on that kind of a workload.