Remove the Puma and OKW basically loses it's competitive ability. The Flak Halftrack, while on paper very powerful, tend to perform rather poorly (hitting terrain quite a bit, unable to clear buildings) and it's mobility is a big issue. The walking Stuka is more or less a mid-late game unit, so that leaves only the Puma to deal with early game pressure.
The Medic truck is nearly worthless for early game as only the support gun can be used (dependent on map and only if your opponent is static). The Puma is the only way to harass infantry and force of light vehicles effectively as OKW and I think it's fine at the moment.
I don't think anyone has a problem with its effectiveness vs infantry or light vehicles, it's that it's also an effective counter to tanks.
It should be bad against *something*.