That's because OKW has major gaps in its stock lineup. No early light vehicle, no proper AT gun, no proper AT infantry, no proper non-super heavy tank and no late game AI tank.
Now some of this could be solved by adding new units, such as the Jagdpanther or tank buster infantry, which would obviously have been preferred. But new models are out of the question, sadly. So all that is left is to look at Ostheer for cross-over units, because that faction has almost everything that OKW lacks.
And these gaps are filled with other units you have chosen to completely ignore.
OKW isn't going to be "fixed" by making it ost with trucks.
Ostheer solutions:
No early light harassment vehicles - 221 (added already)
There is Kubel for map control and AA HT for shock light.
No proper AT gun - Pak 40
Puppchen is full of cheese though with its camo creep, there is also fastest arriving AT vehicle in form of Puma.
No proper AT infantry - Panzershreck Pgrens
Soviets were living, breving proof that you don't need that, current OKW is proof that you still don't need that and 1 shreck is still much more effective then 2 PTRS.
No proper non-super heavy tank - Tiger I
You may not like KT, but you can't ignore it.
Brits do not have such a heavy tank either.
Pershing is very arguable, packs a punch, but can't take any.
IS-2 is a meme for much longer then KT.
No late game AI tank - Brummbär
Obers are a thing.
AI is one thing OKW doesn't lack in at any stage of the game.
I find it only logical to use some of Ostheer's units in OKW commanders to fill some of the major gaps this faction has. It gives players the choice to supplement the faction to their own needs.