This means that you get no accuracy boost for the MSTA-S and in terms of firepower the only bonus is a rate of fire from 4/min to 5/min. Hardly seems worth the extra 25 points, though you do get stronger misc stuff which some might want.
For me the choice is between the Dana and the 2S3M Akatsiya out of these guns. Accuracy vs cost. You get more firepower delivered on target with the Akatsiya, but your target area is larger. I'd tend to go for the Dana myself.
The 'misc' stuff on the MSTA-S is very useful. It has a reasonable AP Gun (great when when vetted), it has a HMG, it travels at 60kph and it 3/1/0/1 armour which can come in very useful. Considering it costs the same as the Dana, but it is part of a larger tree, has a much larger range, almost double the ammo plus all the other points above, I think that this makes the MSTA-S superior, but I suppose it depends on how you are using them.
Did you test the accuracy of the units all at the same range or all at their max ranges? The MSTA-S is accurate even at full range, but at closer ranges it is devastating.