Oh when you said they both worked the same I assumed you meant that they both worked the same ( which isn't the case). What exactly did you mean?
They both require to be stopped to work properly. Ostwind doesn't perform on the move and when you use it as it has been designed for (stationary), it works perfectly fine. That's why I say we could add a setup time for the Ostwind that would probably help people to use it to its maximum potential.
Now Pz4 is simply too good vs infantry and medium tanks. There is absolutely no reason to build either a Stug or an Ostwind when hitting T3 as Ostheer.
I mean, it never cross my mind when I play Ostheer to build anything else than a Pz4 since it is superior/equal to the sherman, T34 and Cromwell. And that's probably the same feeling for anybody playing Oshteer since everyone basically rush for the Pz4.
And buffing reasonably the Ostwind isn't going to change this issue. If you look a the responses given here, many people want the Ostwind be able to deal with LVs and LTs. People want a Pz4 kind that comes earlier (because cheaper) but still able to fight his way vs anything on the field.
If we give some reasonable buff to the Ostwind, nobody will use it because the Pz4 will still be a better choice because of its versatility being good vs tank and infantry.
Look at the Stug, everyone stopped using it the moment it went from OP to what it is today, which is still really good tank destroyer. So that's what is going to happen to the Ostwind, or you buff it to a certain OPness and everyone will use it, or everyone will still prefer the Pz4.
NB: I'm perfectly fine with buffing Ostwind AA performance.