There's a reason why works of art are called compositions. They are by definition composed, with a structure that the creator felt best represented that work.
While I doubt anyone would fault a painter who sketches out her subject beforehand, or a songwriter who includes a chorus between his stanzas, the term "formula" has a negative connotation in storytelling. All formulae have the same purpose: to ensure clarity of message. Yet for other mediums they are considered tools of the craft, while for stories they are considered unscrupulous.