Ok how do you meaningfully define the difference and moreover how would you prevent his version of a "good" silo from devolving into a "bad" one in actuality?

"How does efficient compartmentalization become bad siloing?"

Step one: build Aa and Bb with the A and a people together, and the B and b people together.

Step two: realize you need AB and ab.

Step three: keep the same organizational structure, and try to get the A team to work with the B team ten managers and five hundred miles away.

Data point of one, but it's precisely what I mean when I talk about silos.