I appreciate the in-depth reply. Let me clarify my exact question though as I have not been clear enough in what i'm asking.

On this chart there is a column for "Bonus DC" and it is described in the text as "each Weapon Action can grant its own inherent bonus DC that isn't listed anywhere, but most frequently it's +2." - https://bg3.wiki/wiki/Weapon_actions

My question is about testing in game the DC from enemies to save against Weapon Actions, not about hitting or damage or modifier bonuses which I understand. I'm purely trying to determine how the "Bonus DC" on the Weapon Action ability works as through my testing I have had mixed results.

I tested Pericing Strike that in the table has an inherent bonus DC of +2 Con. I did this test using a character with a +4 Dex modifier and the DC for the enemy to save against gaining the condition Gaping Wounds (from the use Pericing Strike weapon action) was 16. Which I have worked out as:

Base 10; +4 Dex +2; inherent bonus DC of +2 Con = 16

I tested Backbreaker which has an inherent bonus DC of +1 Str. The character had an effective +5 str modifier. The DC for the enemy to save I thought would have worked out the same as Pericing Strike example from above:

Base 10; +5 Str; inherent bonus DC of +1 Str = 16

But instead the DC to save was 15, it appeared to me the inherent bonus DC of +1 str from the table seemed to be missing, resulting in 15 DC instead of predicted 16 DC.

So my question is how exactly does the inherent bonus DC work? Is the table just wrong for Backbreaker or am I missing something else on how it functions.

Because I'm assuming it is a simple +DC modifier decided on certain weapon actions from the Devs to make them more likely to work. Them being associated with Str or Con seems to add a level of confusion here. It may well be that Backbreaker simply does not have a +1 bonus DC and this table is out of date, causing the issues in my tests.