I'd argue that if the Panzer Elite player has any micro skills whatsoever, ACs are essentially uncounterable until the US player has an M8. In other words, ACs are already broken (although I'm not necessarily saying that they're imbalanced - they're not). Not that that justifies the addition of another broken unit, but it's worth pointing out.
What about upping the potential fuel cost of the Flakpanzer to balance it? ACs cost 25, so maybe 35-40 would work?