There is a minimum penetration standard in the current FBI protocols. Expansion is also required to prevent over penetration.
One should not be counting on expansion for anything but preventing/minimizing over penetration.
There is no such thing as magic bullets. Shot placement and adequate penetration to reach vital structures are “it.”
Understandably, 1986 Miami shoot out in which a 9 mm Silvertip went through a suspect’s arm just short of the heart influenced their thinking.
The issues with older 9mm loads were most produced either inadequate or excessive penetration. Particularly when intermediate barriers were involved.
What changed with regard to modern 9 mm loads was bonded /barrier blind bullet designs which have adequate, but not excessive penetration and kept bullets in one piece when passing through intermediate barriers.