The BK9 has a thinner stock thickness, shorter handle and larger blade height which greatly impacts (pun intended) chopping performance.
Thinner stock usually allows for deeper penetration into the media you are cutting and also plays a major factor in weight/balance and the sweet spot for chopping.
The longer handle of Busse's AA means there is more steel (weight) in the handle, reducing its affectiveness in chopping. Combined with a thicker stock, it's actually a lot of steel (weight)!
The BK9 also has a larger blade height that doesn't taper (width not thickness) which means it has more blade mass. This equates to a larger area for the primary grinds which leads to a finer edge (which will cut/chop more efficiently).
Overall, the BK9 has more things going for it that lend itself towards being a much better chopper over the AA.
On the other hand, the AA has more things going for it that lend itself to being a much better fighter than the BK9.
Two completely different knives, designed for different things! Only similarities are the blade length and that they are pointy pieces of steel!
Hope this helps and was comprehendable. I just woke up..
Cheers!