NOTE: this is critiquing the author's 4NF definition (from a link in TFA), not TFA itself.

> If you read any text that defines 4NF, the first new term you hear is “multivalued dependency”. [Kent 1983] also uses “multivalued facts”. I may be dumb but I only very recently realized that it means just “a list of unique values”. Here it would be even better to say that it’s a list of unique IDs.

This is an inaccurate characterization, and the rest of the post only makes sense when viewed through this strawman. The reason 4NF is explained in the "weird, roundabout way" is because it demonstrates [one of] the precise problem[s] the normal form sets out to solve: a combinatorial explosion of rows.

If you have a table:

    CREATE TABLE Product(
      product_id INT NOT NULL,
      supplier_id INT NOT NULL,
      warehouse_id INT NOT NULL
    );

If you only ever add an additional supplier or an additional warehouse for a given product, it's only adding one row. But if you add both to the same product, you now have 4 rows for a single product; if you add 5 suppliers and 3 warehouses to the same product, you now have 15 rows for a single product, etc. This fact might be lost on someone if they're creating a table with future expansion in mind without thinking it through, because they'd never hit the cross-product, so the design would seem reasonable.

The conclusion reached (modulo treating an array as an atomic value) is in fact in 4NF, but it doesn't make any sense why it's needed if you redefine multivalued dependency to mean a set.