I agree it's sophistry, but it does raise deep questions about "what's the starting point for how you are sure you know anything." Plato and the rest apparently took it very seriously, and I guess I can understand why they did, and therefore why Epicurus and the rest had to treat it later on.
Presumably this is also where the Academy descended later into rank skepticism, because they didn't have a better answer to this than "recollection," which very few accept. Apparently that's why both Stoics and Epicureans proposed similar but different solutions.
Also, I see that lots of the Youtube videos spend a lot of time talking about the specific example of "virtue," as if there's something unique about virtue, and that wastes a lot of time. The real issue applies to knowing *anything*, and whether what you think is the truth about something is the full trial, the partial truth, or what. It's the old question about what is "truth?" Do we know truth by example, by definition, or by what "test of truth?"
We need a clear and concise presentation of the problem Plato thought had been identified (and apparently this didn't start with him) and then how prolepsis helped Epicurus respond to the perceived dilemma, along the lines of the article referenced in the first, without falling into skepticism himself.