Energy tells you the volume of the temporary stretch cavity. Hypothetical numbers but lets say 1000 foot pounds gives you a stretch cavity that, at its maximum size, might hold 2L of water. If you can use up that 1000 foot pounds in 10 inches you get a round TSC like a small soccer ball and it will blow up groundhogs into multiple pieces. If you stretch that 2L of TSC out to 4 feet of penetration, such as a trapdoor 45-70 load it will be long and shaped like a party balloon and it will not blow up a groundhog.
Energy is scientific, and there is no arguing with it. The problem is your average dummy only thinks about energy and not about penetration.
Now lets double the energy to 2000 foot pounds which can make a 4L (hypothetical numbers) stretch cavity. This stretch cavity is only about 33% wider than the 1000 foot pound stretch cavity because a sphere increases volume rapidly as its diameter slowly grows. If this amount of energy only penetrates 10 inches it will make a watermelon sized TSC. If it penetrates 48 inches it will make about a 1.5" x 48" long cylinder shaped stretch cavity. If you are talking about "deer and pronghorn" bullets in bottleneck rifles they usually penetrate 18". 2000 foot pounds will NOT drop a deer if it penetrates 4 foot , but it will if the bullet penetrates about 18".
2000 foot pounds with 18" penetration makes a TSC that can, about 50% of the time, instantly knock out a deer. The TSC is so large that it displaces blood and organs as the TSC stretches. This acts like a very strong bear hug and it bursts blood vessels in the brain, resulting in an instant drop.
That is the only thing energy is good for in calculating how good a load is - a certain amount of energy with a shallow penetrating bullet will instantly kill a deer with a lung shot. A load with less energy will not burst blood vessels in the brain and the deer will die by exsanguination. The main criteria for killing an animal is penetration. 5000 foot pounds won't kill an elephant if it only penetrates 6", but 800 foot pounds will kill an elephant if it penetrates far enough.
The volume of the stretch cavity can be calculated directly with kinetic energy. The volume of the stretch cavity has no correlation with momentum or TKO or any other formula. However, penetration kills. A 2000 foot pound wiffle ball will leave a bruise.
You need to first match penetration to the animal. Then you can worry about if you have enough energy for a decently fast kill if you have a heart and lung shot.
A 1200 foot pound foot pound 240 grain 14 BHN 43 caliber at 1100-1200 fps impact speed will make a smallish 3/8" or 1/2" hole with a 1 inch bruise around the bullseye for 4 feet.
A 1200 fpe 240 grain 43 caliber at 10-12 BHN will turn into a 48-50 caliber wadcutter and make a much larger hole and and still penetrate 30". (equal to a 300 Win Mag 200 gr Partition, enough to break big bones in elk)
A 1200 fpe 240 grain 43 caliber that mushrooms to 60-70 caliber will only penetrate 12-16 inches and doesn't have enough penetration to break big bones. The mushrooming bullet would probably kill faster on a heart lung shot with no bones hit.
Here is a temporary stretch cavity:
https://www.youtube.com/watch?v=E8E138NgyFs