Your point being..? That it shouldn't be used by OKW, since OKW is flavored as the later version of Ostheer?
We're not confined to history that much. It being a armored mobile suppression platform in gameplay terms is entirely plausible with regards to historical facts and vehicle weapon specifications.
Sure, there is some role overlap with FlaK HT, but that can only fire when stationary and is quite squishy.
The role overlap isn't with the flak, it's with the unit that is already in the game. I would much prefer something new and unique instead of a slightly crappier ostwind.