Without comparing to a specific bullet, a typical .410 slug from your gun store is 1/5 oz. or about 87grains of lead at 1000fps. So not very powerful at all. Actually very ppor when shooting into a bundle of newspaper compared to other bullets/slugs. When they make the rules for hunting, they consider the specs on the ammo available commercially.
Having that said, I've reloaded .410 for decades and there is almost nothing I've tried that makes a 410 slug shoot any better, further, or more hitting energy. Its just a very poor low powered slug with minimal killing power. Its the perfect chicken gun, but far below adequate for hunting deer.
Yes, I know 45 LC has much better ballistics and energy. However I've never tried it with a full choke 410 shotgun.