The essay is not entirely amorphous
The spirit of the essay [...] is miscellaneous and anti-systematic: "methodically unmethodical," in Adorno’s phrase. Defining the essay is notoriously difficult: indeed it is often suggested that "the one commonly accepted fact about the essay is that indeterminacy is germane to its essence."
An essay can be systematic without being methodical. Methodical speaks to a proven sequence, an A>B>C assembly process, a stale and neutered SOP that will produce a million cookie-cutter versions of the same thing. A template is a method. Essays bloom organically, each idea pulling the writer down a unique path which that idea warrants. Systematic, however, is a much broader term.
Are there not common patterns across essays? Is Montaigne actually unpredictable and anarchic? No, no at all. Of course, he has digressions and contradictions, but to say he is without pattern is to cloud his work in romanticism. Did he not have systems to organize his marginalia and intersperse ancient quotes throughout his works?
Sure, some classic essays are fragmented, but don't we have an equal canon of structured and resolute essays? Are not some of the best essays of the centuries—as noted by Atwan, Lopate, and co.—works of marvelous structure, and is structure not a "system," a conscious inter-relation of parts?
Some essays are miscellaneous, others are focused, some systematic and others not. Why should disjointedness be a defining feature? What is the source of this insistence? What is really meant by "indeterminacy"? I agree with it if it means "essays aren't methodically constructed," but of course sharply disagree that defining common patterns is impossible. Does indeterminacy mean a lack of a conclusion? Some have, some don't.
Each word matters: "miscellaneity" is a fair—but not required— feature of an essayist's larger portfolio, but an essay itself need not be peppered with dozens of unrelated bits. It could be. It could also not. Essay range from cohesion to incohesion, and I do support the surreal, the strange, and irrational, but to banish logic from the genre is false claim and smells of an agenda.