I think this is true for those who keep their own worm bins who can use very fresh castings, like right out of the bin for inoculation purposes. Stuff you buy in bags that have been shipped and processed from who-knows-where, well I'm not so optimistic. Also it's important to inoculate your worm-bins too, with stuff from outside. Soil from the garden, plants and leaves... all that is okay. Hopefully the "good" biology dominates in the bin. I think the worms help tip the balance though
Even without gnats, other lifeforms common in active worm castings are of course springtails. And luckily for predatory mites, that's their second favorite food. So just feed from the bottom, and everything existing at higher trophic levels will take care of themselves. In other words, there is no sense worrying about the entire "food web" lol... just worry about the bottom level. Like capitalism, all nutes are collected and concentrated towards the top. Hahaha