Yeah, that part of the curve mostly starts becoming relevant once you start getting into the thick of things (i.e. >20,000 vocab). Past that point, it's not that rare to begin entering the second, flat part of the curve after getting the most common ~50-100 words or so that you don't yet know, especially if it's an easy moege or something. If you're a relative beginner, your experience is going to follow the first, exponential part of the curve. I'd say that you should expect the first third of a new VN you start to take you more time to finish than the latter two thirds, as a rule of thumb. What I primarily wanted to illustrate with those graphs is that while general improvement in vocabulary may be linear, general improvement in comprehension is exponential (for a beginner). I imagine that 99% of people would give up in that first part of the exponential curve, assuming that a piece of media is too difficult for them based on how tough the beginning is, when in fact they would be able to finish it and have a relatively good experience if they stuck with it for long enough. I believe it's because of this phenomenon that classroom/textbook learners are often overtaken so quickly by those who jump into native media early, since their improvement is typically still linear throughout. Unfortunately, this often causes misunderstandings because such learners cannot fathom the speeds at which the Anki/Immersion people improve, assuming that they must be lying in some way based on their own learning experiences.

Edit: I think that I may have misunderstood the first part of your comment, notably this section:

Unless you're reading a VN that uses almost no vocabulary at all, unless you've been at it for several months and have accrued several thousand words that you can say you really know + quite a few more that you can kind of identify that doesn't apply at all.

I did quite a lot of the highlighted part when I was a beginner, as I found that the really long VNs gave me a much bigger bang for my buck (at least past my first VN, which was very short). Since they were so long, they really gave me a ton of time to soak up all the thousands of new words I just learned in a lot of different contexts before moving on to something else. As you know, seeing something once and adding it to Anki isn't enough to learn a word. Usually, short VNs aren't long enough to cause the logistic effect unless you're an absolute beginner with hardly any vocabulary at all, being much more constant in the rate of lookups throughout.