It's impossible to write a script without structure (in the abstract sense). If a writer were to create a script without structure, its structure would be structurelessness. And the reader or viewer would impose a structure onto the result (much as we see a figure in a random cloud or a constellation in the starry sky).

The problem of formula occurs when a particular guru (whether a professional theorist or a lay person) states that in order to be effective, a script must have this or that structure i.e. grid or template).

Structure is a process that unrolls in the audience. We watch movies to be part of the process, not to imbibe the formulaic result. Otherwise we wouldn't need to see more than one movie that fits a particular formula as prescribed by the guru.

To be involved in the process, the audience needs to perceive both an underlying formula / grid / template that the audience already knows and at the same time needs to be surprised by something that is new or unexpected. Plus all the other good stuff described in The Protagonist's Journey.