I'm not sure what "9.5 Sharpness" is, but the 31A is sharp for a telephoto zoom
from the 1990's. It is not going to be as sharp as a decent prime or the DFA 150-450. I had the original Sigma 170-500, and I find the 31A to be a bit sharper.
The lens has its flaws: wide open is not that good, especially at the long end. There is CA and PF. Spherical aberration makes the lens soft, glowy, and low-contrast inside of 10 yards unless stopped down to f/8 or smaller.
When used with respect to its weaknesses, it's a good performer.
w/1.4x TC
430mm-ish, wide open
heavy crop