Seriously, “few” USUALLY refers to number and “less” USUALLY refers to size or value. However, there are many perfectly acceptable exceptions to this rule in current usage, because as noted above, the language is dynamic and evolving constantly. So it’s kind of a moot point, especially when arguing with a few less smart people on the internet.

A lesser mind might disagree with me on a few points,
about which I could care less.

In a case like the one you describe, quote away and let him bear the consequences.

Matthew:
Thanks for your response. It is obvious now.

My examples illustrate the consistent distinction between “less” for the uncountable & “fewer” for the countable, just as, heading the other way, we use “much” for the uncountable & “many” for the countable, or are you about to say “Since I got paid, I have many more money”?

The choice between them is semantic, not purely aesthetic. When we use “fewer”, we refer to something countable. It is not simply a sound. You admit as much when you state that using “fewer” “keys the listener/reader to listen [or read] for the number”. There are no two words in English that mean precisely the same thing, although colloquial use frequently blurs meanings so that one word can appear interchangeable with another.

(Your example, “fewer fits in less situations” is inaccurate. Try “fewer fits in fewer situations”. The moment that you make “situations” plural, you make them just as countable as fits.)

Your guideline, which word “flows smoothly” is redundant. The guideline exists: “Less fruit, fewer oranges”.

Wallaby, your Webster’s unabridged describes how people use the word. We are describing a nice distinction between two words.

Arvy, your sentence using “less” with counting nouns (“It’ll take less than two hours”) still uses less for the uncountable &, in that sentence, understood “time”. Your sentence isn’t saying, “It’ll take less hours than two hours”; it’s saying, “It’ll take less time than two hours”.