the translation I watched [subs, as intended] was kinda not the best. It had "mushi" translate as "misshapen spirit", but imho, a better one would be "formless spirit". [iirc, 'Mu' in this capacity is 'void, empty, without substance', with 'shi' being 'spirit, ghost, or similar being'] Perhaps 'incorporeal beings', since the entities in question have a fixed and consistent perceptual nature [eg, if you are naturally able to see them, you can identify them by appearance, even if you cannot interact with them meaningfully--likewise people who drink the golden sake can see them, and should be able to give reliable descriptions. This means they have "form", but lack corporeation-- they are not physical beings.] "Mushishi" seems redundant in the use of shi. maybe I am just mistaken. [shrug]
the series translates the experts as "mushi men". I was confused, because I kept listening for --tachi, but never heard it. It could be wordplay that the experts are themselves supernatural beings, just ones that do have a corporeal form. [no spoilers about the protag. Just this shoutout- he's not quite normal.
] That might explain why the villagers that strangely do know about these experts treat them suspiciously/nervously.
as for the "sheer numbers" statement, I meant it in the sense that 'even if only 1% cauxe trouble, the fat that no matter where you look, you will find them, and in large numbers, means interactions will be frequent enough that the experts will be well known and consulted regularly." see western parallel with Germanic Volva. Instead, these experts are instead themselves obscural in their presentation-- only really old people know about them, and almost universally speak poorly of them, which seems really odd to me.