Ever play One Down? 
I did on launch, exactly one year ago, and got my mask on the 12th of October (headshot multipliers were buffed on the 16th). It was not enjoyable at all, nor was it difficult. It was just annoying at best. The main unit (ZEAL Heavy) was a bullet sponge that dealt 225 damage across the map with no falloff. This alone limits the amount of viable builds to a number I can count on one hand. In order to beat the difficulty, all the player had to do was equip rogue and suddenly it was nearly identical to Death Wish.

Why does this happen?
It has to do with player damage and how it works. When the player is shot, they go through a grace period where only higher damage can get through (this almost never happens on OD). If this does not happen, the player is more or less given invulnerability for the duration of the grace period. This also occurs when the player dodges, meaning every successful dodge grants the player 0.35s of invulnerability.

Okay, so what? Why are you telling me this?
In Payday the Heist, this was the big change on Overkill 145+, and the reason you get annihilated so fast. The enemy damage actually never changed throughout the entire game (however your armor did drop depending on difficulty, it was the same amount on Overkill and Overkill 145+). The grace period here was 0.15, meaning that this invulnerability only lasted 0.15 seconds, instead of the 0.35 seconds we currently have now on Mayhem through One Down. This allowed them to make it so the player wouldn't get downed in 2-3 shots, but being out of cover would be punished more, much more, in fact. It is a much bigger change than you may think.

So is there a solution to the current problem at hand?
One where we can get rid of the huge flaw in One Down that limits so many builds? Well, I think you know where I am going with this. We first lower the amount of damage dealt so that it is less stupid, but we also lower the grace period to compensate. The result? The player is punished for being out of cover (to be honest it seems like you're punished more than vanilla OD) but gone are the days of getting killed in 2-3 shots across the map because the units don't have any falloff.

This does not have any restrictions on it, as from my experiences playing it I feel that it is just as hard (if not harder) than vanilla One Down. Remember that damage is client sided and will not affect people that do not have the mod installed. However, you may wish to avoid using this in public lobbies or with friends that are not comfortable with you using it. Also note that this mod does not fix the other issues present in vanilla One Down, such as the bullet sponginess and the insanely high spawn rates (however it is compatible with this mod. This only adjusts the damage which I feel is the most unbalanced aspect of it. The (very high) accuracy of the enemies is unchanged, as I feel a super elite DHS death squad should be very proficient with their weaponry. The enemies will now fire in longer bursts depending on how close you are to them, where being in their face results in them full on spraying.

Note that for Bulldozers to have weapons other than the pump shotgun you need to install Enemy Weapon Fixes.

Here are the values changed (only affects One Down):
Grace period: 0.35 seconds to 0.15.
ZEAL Heavy: 225 damage to 50-150, depending on range (average is about 75, 10 meters).
ZEAL Light: 62.5 damage to 40-75, depending on range (average is about 65, 10 meters).
ZEAL Shield: Unchanged (70 damage all ranges).
ZEAL Cloaker: Same as ZEAL Light (vanilla damage is pathetic).
ZEAL Bulldozer (Pump Shotgun): Unchanged (a lot xd).
ZEAL Bulldozer (LMG): Set to the same as Death Wish (100 at all ranges).
ZEAL Bulldozer (Saiga): Set to the same as Death Wish (105-240, depending on range).
Taser: Same as ZEAL Heavy.
Medic (Assault Rifle): Same as ZEAL Heavy (sorry but Medics do terrible damage in vanilla).
Medic (Pump Shotgun): Unchanged.

If you feel like responding something along the lines of what is in the preview image, or that it is okay to leave the difficulty unbalanced, please read this first. Otherwise you're just wasting your time.

v1.03: Fixed Gensec Elites/Murkies with UMPs not scaling properly and doing pathetic damage. Made the enemies fire in longer bursts depending on how close you are to them (very close = full on spraying).
v1.02: Added compatibility for 'Pre-Difficulty Rebalance HP Values' http://modwork.shop/19290
v1.01: Fixed a bug where Phalanx HP was not set correctly.
v1: Initial Release.