Epistêmê cannot just be a matter of knowing a logos. Knowledge, it appears, is demonstrated not in the knowledge of any particular logos, but in the ability to defend a logos against refutation. It is precisely the latter ability that is characteristic of epistêmê. This ability, furthermore, cannot be imparted by means of a logos. For, no logos suffices to endow its possessor with the ability to defend it (i.e., the logos) against refutation.
Given that Plato appears to have believed that no knowledge of a logos—no matter how elaborate the logos—is sufficient for epistêmê, one can see why he was drawn to describing epistêmê as requiring a direct intuition of Forms. One can also see why he was inclined, in describing such direct intuition, to use the language of visual perception. When I see an object, I can describe the object—or answer questions about it posed to me by someone who does not see the object—but no logos that I can give exhausts the content of what I see. It is true that some contemporary philosophers would take issue with the claim that the content of visual perception is non-propositional. However, it is not implausible to suppose that Plato thought of the content of visual perception in this way.
Vlahovic, Denis, "Plato on Episteme and Propositional Knowledge" (2005). The Society for Ancient Greek Philosophy Newsletter. 442.