Disclaimer, this is not targeted for vanilla New Vegas. This is intended for a game where your player has much lower health so he dies much faster.

In vanilla New Vegas, enemies are generally as hard as they are at level 1, as they are at level 50. There are some cases of leveling, even done in a cool way such as Veteran Rangers showing up in the higher levels. While this approach is not very arcadey, I prefer it. Why does fighting a mole rat have to be a bullet-sponge-a-rama? Mole rats are weak, they should never pose a challenge unless there are 500 of them. Enter the New Vegas DLC, where Obsidian abandoned the vanilla approach and introduced leveled enemies. Think of Fallout 4. If you're level 3, this robo-scorpion will die in a few shots of a decent rifle. If you're level 50, not even a high explosive missile out of Annabelle will get the job done. I mean, there are leveled sewer rats that can have the same health as the sentry bot. WTF? They didn't feel the need to level out Gabe or the Think Tank, they are the same across all levels. I play with a low health mod, meaning weapons and armor maintain their damage and ratios, but I die faster. It's meant to make it more "realistic" or more of a "survival" game. So when I go through Old World Blues at level 50, with the same health I had at level 20, I am consistently one shotted by enemies I can't seem to kill without explosive rounds out of the AMR with a sneak attack crit. So here is my attempt to fix it.

TLDR:
Enemies have consistent health at all levels, and in some cases damage too. Bosses have double health compared to the regular versions. If you are playing with un modded gameplay, this is simply going to make killing everything in the DLCs easier past level 10 or 20 or so. This is intended, because I play with a low health mod so I am also much easier to kill.

Full Details:

Dead Money:
Ghost people have had their perception set to 2, and health to 150 (Trappers to 225). This is the same health as playing at level 20 vanilla, with the perception fixed from 0.

Honest Hearts:
Honest Hearts uses a kind of similar levleing system to vanilla, so I didn't change much at all. I did lower the health of spore plants and spore carriers slightly as I did find they were a bit spongy. No other changes.

Old World Blues:
Cazadores were made like vanilla.
Military and Police Cyberdogs had their health lowered to 100 and 75 respectively.
Mister Gutsy and Mister Handy were made like vanilla, with Mister Orderly copying Mister Handy.
Nightstalkers were made like vanilla.
Protectrons are slightly stronger than vanilla at 75 health vs vanilla's 45. Construction drones copy them.
Robobrains were made like vanilla.
Robo-Scorpions past level 10 have been neutered. 200 health for any regular and 250 health for a "b" variant. (Vanilla at recommended lvl 30 was 525/600)
Securitrons were made like vanilla.
Sentry Bots were made like vanilla.
Rats were made like vanilla.
Spore carriers appear in a different way, with different variants appearing at different levels. I rounded out the higher levels so it isn't as spongy.
Spore plants were set to 100 health. This is in between the weak vanilla version, and the spongy DLC version.
Giant Robo-Scorpion was fixed at 2500 health, the same as level 30 vanilla.

Lonsome Road:
Deathclaws were made like vanilla.
Mole Rats were made like vanilla.
Sentry Bots were made like vanilla.
Turrets were made like vanilla.
Eyebots were set to 125 health, lower than the starting default.
Glowing Trooper Ghouls were made like vanilla.
Tunnelers were set to 200 health and set attack damage at 50, lower than default. Hulking ones are slightly stronger and venomous ones are slightly weaker.