Brewer's anything is a by-product of human processes. Why get one vitamin at a time from by-products rather than getting a bunch of healthy vitamins from real foods?
"Holistic food" is just a term loosely used to describe food with whole ingredients, not parts of ingredients or chemicals. Holistic foods usually have less/no filler, less/no by-products of human processes, less/no short cut ingredients, like beet pulp which hardens the stool chemically or corn which boosts the protein and carb content of a food even though a dog doesn't digest most of it.
Before you swear off holistic foods, you should take a look around the dog food forum here. There are a lot of links and ingredient lists around to look at and compare your food with.