You actually answered it urself! player invest his mp into squads as soon as he has manpower for it! that's the thing, since OKW teching is very cheap and the factions doesn't generally give u options for various support weapons such as mgs/mortars etc you build another (very cost efficient) squad (which u can upgrade it to the mighty shreck).
OKW stays broken as long as it's easy to shreck blob, or shreck has such a performance
In the preview OKW teching costs are pretty much similiar to the USF teching costs. I personally don't blob schrecks and rarely build them, because good players know how to deal with them. In addition I rather invest munitions into mines and grenades, while letting my raketenwerfer deal with tanks.