The basics of that study was 3 days of rest to 4 days has no impact either way. What it did do is watered down the pitching.
Here is the thing: pitchers are trained to pitch every 5th day now. Taking a pitcher and shortening his body's normal cycle would most likely result in injury. This is something that should be started in the lower levels if they went there. But they never will with the investment going on to major league players. No owner wants to end up paying a broken ace for years after he blew up his arm by adding work load they never had before.
It is much easier to lessen vs add work.