Do we actually know that armor piercing means that bullets go through guys? I mean it sounds like it, but how do we know for sure?

That first post, at least, didn't do the kind of analysis I was hoping for. Basically we're getting a lot of guns buffed by 30% and then on red bars we're looking at a 50% decrease in precision damage. That might leave a good bit of wiggle room depending on how much damage it actually took to kill a red bar. For instance:

Start with the most extreme example, a high impact Sniper Rifle vs a plain red bar Thrall. You're not doing just barely enough damage to kill that Thrall when you get a headshot, you're doing probably several times more damage than necessary. In this case, you're probably overkilling the target by something crazy like 200% or 500%. A 20% decrease in precision damage just won't matter in this most extreme of examples.

Now, scale it back. There are probably times where you can kill something like a Vandal with one headshot from a heavy Scout Rifle. Again, you probably aren't matching the target's hp with your damage, but you're also not overkilling it by hundreds of percent, either. So... in typical combat, how much do we tend to overkill red bars with things like Bows or other one shot kill primaries? If we typically overkill enemies by 20% or more, then you still won't see a change. I'd guess this will be true of Bows which always seemed pretty powerful shot per shot.

Scale things back again to a worst case scenario. Maybe a light Auto Rifle or SMG takes 10 precision shots to kill a red bar? With this +30 - 50 thing going on, you'd be looking at now having to hit with 12 bullets instead of 10. That's not the end of the world and is on the border of not being noticeable in the heat of combat.

I'm imagining a typical scenario where you've got something like a Hand Cannon vs a red bar Cabal and it takes 3 headshots to kill them right now. Again, you can't just add 20% to the number of shots needed without first looking at how effective you really were before. If those three shots were each doing 40% damage, you'd do a 40%, 80%, 120% overkill and this +30% - 50% thing would again cancel out even where it's not immediately apparent.

Ok... whew... somebody actually started doing some testing...

Decided to test this because I was curious. Numbers from tribute hall, so there may be some inaccuracies, but the difference is pretty massive regardless.
A red-bar thrall in the tribute hall has ~14,000 health, from what I can see. A headshot from a precision frame bow on perfect draw does 66,639 damage, effectively killing it 4 times over. Even without the damage buffs and the removal of the 2x modifier, that's still doing twice the amount of damage as the red-bar. Yes, thralls are some of the weakest of the red-bar enemies, but think bows will do enough damage to one-shot most trash mobs comfortably.

Ran some more tests. Unfortunately, had to use lost sectors since dregs/legionaries/acolytes etc. are all majors in the tribute room for some reason, so the numbers might be off.
Legionaries (lost sector in cistern, nessus): ~1200 total hp, crit w/perfect draw is 3206
Incendiors (same location): ~1600 total hp, same damage on crit
Vandals (The Empty Tank, Tangled Shore): ~4800 total hp, 16,261 crit
Dregs (Same location): ~2400 total hp, 16,261 crit
Acolytes (Wolfship turbine, tangled shore): ~3,800 total hp, 16,261, crit
Knights (Jetsam, Tangled Shore): ~6900 health, 7220 crit

We'll still need to watch this. Partially because Bungie doesn't have the best track record of even making the changes they say they are making. But also because it may be fine for enemies that you are leveled with, but in edge cases like Nightfalls or Raids, you might actually be at enough of a disadvantage that it will take an extra shot even from something as powerful as a bow.

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Keep in mind, the back end has been changed too. All our referencing of numbers is for a back-end that is no longer the same, but seeks a parity in result. All intents and purposes, to me it seems we're just getting Destiny 2.5 over here. Unless we know the exact changes made to the back end, we can't compensate for the discrepancy. Buff? Nerf? We're going to have to feel it. Math alone isn't going to help us on this one, as there isn't enough data to math it proper.

Not that it's going to stop anyone from trying. (Clearly.)

Would it be so wrong to read the Directors Cut with fresh eyes?

(Director's Cut - Part III)

Destiny 2 was built with very different goals in mind than was the much-improved version of the game we’re playing today. Some parts simply weren’t meant to last for several years. One of those parts is the displayed-damage values relative to the player’s Power level.

This problem most clearly manifests to players as the frequency of “999,999” showing up in your HUD. As the post-Forsaken year continued, the curve that dictates the value of displayed damage sharpens into a hockey stick. The display values for Shadowkeep rocket off the graph and become almost vertical!

This inflation for damage is getting retooled this Fall. It will look like a UI numbers squish, but more crucially, behind the scenes we’re setting up the damage-display system to last. It’s important that you understand we are not nerfing your outgoing damage; rather, we’re refactoring the displayed number game wide.

We’ve also had something that, over the years, the team has come to call “The Immunity Wall.” This is a value where players cannot damage AI. In the game today, if you’re 50 Power below an enemy and you shoot it, you deal a big ol’ donut. Another change we’ve made for fall is that we’ve lowered (raised?) the immunity wall to 100. This means you can now deal damage to enemies you are up to 100 Power below. The at-Power (you and an enemy are the same Power) experience isn’t changing. This isn’t a nerf. This is a way for folks to take on greater challenges by fighting further below the Power curve.

(Bold, italics, and colors within Director's Cut quote my edit.)

Intent of action has been stated. Delivery prepared. But will it be in pristine order, or feel like someone played football with the package? Well... that's what we'll be finding out October 1st.

*why are they making poor shooting less punishing

FTFY.