Because medium tank at 8-9 minute is such AWESOME idea.
Why won't we put sherman to LT tier and T34 to T2 as well?
Rushed shermans are a thing that already exists.
I agree that Elite armor is garbage, but OKW does have a medium, the Panther, it's just that it is a really expensive medium given the fuel penalty. It doesn't matter much in a 3 or 4 but in a 1v1 it means that it comes really late, and you always have to chose between JP4 (or Puma if you went mechanized) or being vulnerable for a long time if you're waiting to build Schwerer and Panther.
That's the issue, OKW has a huuuuuge gap in it's mid game thanks to 1 tier being nothing but light vehicles that start dropping off in usefulness when AT guns hit the field en mass and the other doesn't offer good AI options.
The Panther really isn't a generalist medium, it's a heavy tank with some sprinkled on AI for all intensive purposes.