Ostheer is not in a good place right now, OKW is fine. Other than that I don't think there's that many major balance issues. Ostheer could use a few buffs here and there, such as Pgrens, Assgrens and Grenadiers.
Ostheer has many strengths but in my experience the core difficulty is scaling infantry into the late game, since Ostheer lacks the elite infantry that OKW has that allow you to stay and compete. Ostheer vehicles are in good shape though, maybe a buff to the Ostwind or a price reduction is in order.
I've been playing a lot of Ostheer lately and trying to make it work the main issues are with your core infantry just not being able to keep up into the late game.
I don't think "allies OP" is the issue, it's that Ostheer has glaring weaknesses that need to be addressed.
The statement is self contradicting. Ostheer is the benchmark. If the faction has glaring weakness than other factions are "OP" and should be brought down to Ostheer level.