The Su-39’s payload (weight) matches that of the A-10, but, I think the A-10s payload is rather limited compared to even the Su-25 (which can carry overall less weight than the A-10, but when the does A-10 really leave fully loaded?). (ARMs, Various ASMs)
Comparing payloads (weapons) of the A-10 to the Su-39 is a joke. The Su-39 can carry upto 6 Kh-31s (AS-17)… and more… that’s pretty damn good!