but you also seem to be implying that if we accept the first then the second never holds, and that can't be right.

Ah. I can see how you might infer this from my post, but I definitely do not endorse that if we accept the first than the second never holds.

It is useful in many cases to talk about concepts in terms of necessary and sufficient conditions. I use stipulative definitions like this all the time. But stipulated definitions aren't the aim of "classical view" conceptual analysis.

The examples you give (of typicality effects and so on) are examples of concrete, everyday concepts (bird, fruit, fish, furniture), when really the argument you want to make against the classical view of concepts is about much more abstract concepts (knowledge, truth, justice).

Like I said, my post is already too long, and I provided references if you're interested to read more studies on typicality effects.