I think an OKW trying to save fuel from not purchasing tanks does leave them very vulnerable. The raketenwerfer is pretty rubbish and sometimes it can even be killed in one shot from a Sherman. Volk Shrecks aren't really good at killing tanks unless the enemy tank wants to stick around too long but there is a better chance of the tank wiping out the volks squad than dying.
The OKW doesn't have a lot of equipment that can take on buildings no flame throwers or mortars, I don't see the 75mm howitzer performing well against buildings. The Stuka is pretty much the only thing the OKW has against buildings but even then it's 100 fuel, or 150 fuel if you count the fuel decrease.
Double (or more) OKW teams are "easy" too handle. As you said, the faction has a lack of certain units.
I see OKW as a faction for camping a fuel point, defending it with a couple of subpar AT units (schrecks, racketen, Schwerer Panzer Truck, etc), and trying to harass enemy points with a lot of elite infantry while waiting for the almighty KT to appear for a final push.
The issue is that Ostheer makes up for all the things OKW lacks, and then what it was a desesperate fight for holding map until the KT arrived, turns into a impenetrable wall of MG42, Paks, elite infantry, etc, against which allies can only hold until midgame.
Is then when panzerschrecks really shine, because they are always the decisive factor in the fights between heavy tanks. So, even in the case you have an ISU-152, an IS2 o plenty of Jacksons so fight their KT, Jadgtiger and Elefant; volks and pgrens will always incline the escale to the axis side, giving extra damage from the sides.
Allies have really a lot of trouble dealing with armor lategame. They don't have specialized AT infantry, nor AT emplacements like Pak43, their AT guns are overall inferior to the axis ones, and finally their Tank Hunters lack armor.
It is not strange that axis dominate lategame with these odds against.