What I think I saw in the past was each route quoted in percentages of historic performance of time keeping, an average over say 6 months or a year. Maybe I imagined that?
At this website you can search historical on-time performance, connections, etc. for any Amtrak train.
You can see the history of the train(s) you are interested in. https://juckins.net/amtrak_status/archive/html/home.php