I'm not saying it's not powerful against ostheer, just that it is still a T3 level unit in terms of unit value. While it is obviously better at things then the other TDs, debatably more important things, it isn't a T4 unit in terms of value. As in it isn't on the same level of power as panthers, brumbars, or KT.
For example, T34-85 and sherman 76 are actually better then their T3 counterparts. On the other hand a Jackson will will actually lose in a head-on fight against a jagdpanzer or su-85, other T3 level units.
Ostheer's weakness to it has much more to do with not having a proper TD themselves to fight it. I know can be hard to kill good player's jacksons with infantry AT.
Fair enough maybe your right. perhaps if the stug III gets reworked into a TD with 60 range OST T3 might become more viable against USF.