Neither.
Reading my posts should make it clear that it is not. If you have read my posts up to this point and find it unclear what my argument is, I'm afraid I can not help you understand, so you'll just have to move on.
For the final time, as clear as I can think to say it: The DM's choice does not offset the effectiveness of the feats - it determines it.
There is no scenario in which the DM's choice of monsters doesn't affect the effectiveness of these feats, so it is not some special, deliberate action to choose monsters in a way that affects the effectiveness of these feats.
I"m sorry, but could you actually explain the effective difference between what I said and what you said? As I take it, you're saying that DM choice determines how effective the feat is -- that by making some choice A, the feat is more effective, and by making some choice B, the feat is less effective. Assuming that you mean the choices the DM makes are intentional and not random (making this statement equivalent of saying the dice sometimes make the feat more effective and sometimes less) then how is that functionally different from me saying that the DM chooses intentionally to improve or reduce the effectiveness of the feat? I mean, if you go with how I said it, the outcome is that the DM can make some choice A, and the feat is more effective or could make some choice B and the feat is less effective.
I'm completely flummoxed as to why you think what you just said is any different from what I said. I can only guess that you want the more neutral wording of 'determines' over the less neutral wording of 'offsets' because the end result is
exactly the same effect.
Let's take a moment to recall that this sidebar occurred in response to me saying that the average AC was 15ish in the game, across all CRs. You took exception, which I now understand is because you're saying that this average isn't truthful because some DM may choose a set of monsters over play that has a different average AC. I was making my point not that this isn't so -- it's trivially obvious -- but that the average AC across all CRs is indicative of many choices with lower ACs. I then took your statement to be an objection that this spread has any effect, but I now understand that you're entire argument is a semantic one about the fact that a given DM's choices over a game will have a slightly different (or, if very outliery, a noticeable) difference in that average AC. Which means you're just making a general argument about specific possibilities. I didn't twig to that because I generally expect that people understand that you can logically argue from the general to the specific (all Bobs are tall --> Bob Smith is tall) but not from the specific to the general (Alice Smith is tall --> all Alices are tall). Frankly, I'm now not certain why you wasted so much time getting to this trivial point. It's uninteresting.
No, if he's not intending to select the creatures, then it's, as I said, a random occurrence like dice rolls. Taking my arguments in pieces instead of in context to dismiss them is bad pool.
However, I see now that your argument isn't this, but rather than different DMs will pick different monsters across their games, and as the average AC across CRs may not hold. You can have that argument, it's uninteresting.
Yes, I could have offered up an apology for your mistaking me with your accusation of misrepresentation. Perhaps you should ponder why I didn't.
I have some ideas, but you won't like them.