You don't get it Country1. When they measure velocity and energy, it's after it left the barrel. Which means whatever was lost, has not been measured because it has no relevance. The relevance of that fact has no bearing to anything like you claim.
The measurements are taken at the point of impact at certain distances, and those numbers are the raw numbers used for comparisons. Any energy lost was lost before the important data was collected.
The numbers gathered by the major ammo manufacturers, the federal agencies that make firearm recommendations, and just some TV show people who like to play with numbers consistently show that the .38 +P rounds have less energy and velocity compared to 9mm rounds across the board when using similar rounds.
That's why the .38 caliber should be considered after the 9mm to the .45 ACP crowd. They are more effective rounds assuming you can control them reliably.