I'm not aware of any good single-number lethality measure for small arms. It's just way too complex to boil it down to a single number. That's true whether the number is a scientifically significant and verifiable quantity like Kinetic Energy or Momentum, or whether it's a number generated by a formula that someone like Hatcher or Taylor made up.
That said, Kinetic Energy is absolutely not, by any means, "pseudo science". It is a scientifically verifiiable quantity relating to the potential of a moving object to do work. The fact that it isn't a good measure of lethality doesn't mean it isn't scientific, it just means that it doesn't provide a good measure of lethality. One might as well say that because the weight of a firearm doesn't provide a good measure of the firearm's lethality that weight is an outstanding example of how pseudo science sells.
For a time in the in print community, both momentum and kinetic energy were being used as measures of lethality, but kinetic energy won. Both groups wanted to be able to sit down at their typewriters, pull out a slide rule, and calculate lethality using the Newtonian laws of motion. Humans are always trying to find patterns to predict the future, it is just the way we are. By the way, for over a century economists have been trying to reduce economic predictions to a precise mathematical science, and they have failed. A very good reason economics is called the "dismal science". Everyone would love to have their area so nicely and neatly concise and predictable as the Newtonian laws of motion.
What you read in the popular in print press is dominated by commercial concerns trying to sell new cartridges and new guns. And they mis use mathematics and the Newtonian laws to push product. I contend that kinetic energy as a measure of lethality, won over momentum because it is easier to push a bullet faster than to increase momentum. Kinetic energy is mass times velocity squared, momentum is mass times velocity. Just increase the velocity ten feet per second and the latest and greatest cartridge is a hundred times better than the old!. Whoopee!!
Kinetic energy is real, momentum is real, ions are real, frequencies are real, crystals are real, but the tables of kinetic energy needed to kill a mouse, a deer, an elk, an elephant, that was pretty much psuedo science. And the sales pitches of cartridges, based on kinetic energy, the whole pitch was pretty much pseudo science.
If anyone wants to see how ions, energy, crystals, frequencies, which are all real things. are used in pseudo science advertisements, you need go no further than the products that Gwyneth Paltrow sells on Goop:
Wearable Stickers that Promote Healing
https://goop.com/wellness/mindfulness/wearable-stickers-that-promote-healing-really/
Jade Egg
https://shop.goop.com/shop/products/jade-egg?variant_id=25156&country=USA
ahem...