It's a little more than just the mortar that's an issue. I consistently run out of gas around t3. I can have 3 vps and both fuels, but rifles blobs with tank support just rek everything in their path.
Yes, that's why I suggested minor buffs to t3 units. I also don't believe you'd be having problems dealing with US tanks if you hold both fuels. When discussing OH t3 people tend to overlook the Stug and forget just how good it is for the price, especially if you can get some vet on it. That's another reason I suggest a slight buff to the Ostwind, so the Stug can be used to its full potential in the AT role.
It's true that the game has been moving away from axis lategame dominance, but that's a good thing - the whole 'X faction must win in 15 minutes, Y faction must stall to late game' mechanic isn't satisfying and makes it impossible to balance both large and small matches. Of course if a faction is losing their advantage at one point of the game then we need to look at other stages (in this case the mid game) to make up for that.