I think we need to make a distinction between a stereotype and an archetype here. The two are often confused, as illustrated by Wikipedia's unhelpful definition of a stock character:
A stock character is a stereotypical person whom audiences readily recognize from frequent recurrences in a particular literary tradition. Stock characters are archetypal characters distinguished by their flatness. As a result, they tend to be easy targets for parody and to be criticized as clichés.
Archetypes are the building blocks of stories. Stories are particular constructions of human experience that produce an emotional response in us. We are wired for story. Archetypes are the anchors of key human relationships: hero, trickster, monster, mother, lover, etc. There is no story without archetypes.
Stereotypes, on the other hand, are lazy portrayals of characters, relying more on appeals to prejudice than on appeals to the recognition of the truly human. Archetypes must be fleshed out, and the lazy way to do this is to rely on stereotypes.
Stereotypical characters can appeal to readers by appealing to their prejudices. This is not a literary effect, but since it is satisfying to have ones prejudices confirmed, it may sell lots of books.
A properly fleshed out archetype, on the other hand, is essential to producing a satisfying literary experience.
You might use the term "stock character" to describe either one of these, but the effects and the merits of each are worlds apart.