Actually a single at gun isn't able to stop T70 either. It all depends on positioning.
It's not exactly the same. A single AT can not kill a T-70 but can prevent its aggressive movement in some certain area well. But Ostwind can deal a lot damage from distance, meaning that even u have a AT in front of the Ostwind, it can still bleed u hard. And the biggest difference between them maybe when counter AT infs. PGs or Fusilers with 2 shercks can defend them from T-70s while Guards or bazooka teams are wiped out quickly by Ostwind.
Nerfing it's range or far aquracy is reasonable.