I get the price point, but what do you mean about mobility? Su85 and firefly are both pretty slow, but FF at least has turret
It also has more damage per shot and that improves with vet, so its gun is better in some sense anyway
More damage per shot but less damage overall due to super bad reload. SU 85 (5.7/2.1 and 6.8/2.5 with vet) is also faster than FF (5.3/1.6 and 1.8 with vet). Again FF receives no significant speed buff with vet, same as penetration. I wonder why?
And saying SU85 is slow is wrong, it has more top speed than Jackson at vet 3. Jackson is much faster without vet but gets no vet speed bonus so the SU85 ends up faster in the end.