I think I understand this "Cartesian product" reasoning behind 4NF/5NF, I just find it irrelevant I guess.

Cartesian product is explained in Kent: case (3) in https://www.bkent.net/Doc/simple5.htm#label4.1 ("A "cross-product" form, where for each employee, there must be a record for every possible pairing of one of his skills with one of his languages")

I do not explicitly mention this Cartesian product even tho it is present in both posts ("sports / languages" in 4NF, and "brands / flavours" in 5NF).

> it demonstrates [one of] the precise problem[s] the normal form sets out to solve: a combinatorial explosion of rows.

I just don't understand this wording of "a combinatorial explosion of rows" — what's so dramatic here? I don't need four iterations of algebra-dense papers to explain this concept, I think it's pretty simple frankly.

And my implicit argument is, I guess, exactly that you could design tables that handle both problems without invoking 4NF and 5NF — people are doing that all the time.