Those loadouts are not possible IRL and should not work in the SIM. You can only mix magics and 530D or magics with 1 A/G ordinance (no bombs + 530 or rockets + bombs or 2 types of bombs).
If it currently work it's a bug, and it should be fixed.
And I don't agree with your analysis, to me, the efficiency of an A/G platform is not determined by the number of target you can destroy, but by the dedicated systems that the plane have to help the pilot deliver the weapons.
IMO the viggen is a far superior ground attack plane, due to the A/G radar, the weapons (BK-90 OP as f*ck) the INS and general systems of the plane that allow it to be used in a high threat environment far easier than the Mirage. The only thing that the Mirage have better than the Viggen is the D2M (MWS), but if you fly in pair, you can reduce the probability of an undetected manpad launch.
That's only my opinion regarding my experience using the two aircrafts :).