This doesn't seem like logic that one could apply. OKW does not have anything to do with coh1 campaign.
Nah, it's fundamentally how the game is designed. Hence why COH 2 isn't realistic but focused on squads, soldiers, individual models, few armored vehicles; and not a whole division of 10,000 men attacking together in a map. Very war movie-esque style of gameplay compared to MoW which is more of a ww2 sandbox game where you can use all sorts of cool stuff like super pershings and so on.
COH campaign might not have anything to do with COH 2's development. But the resemblance of some scenes in COH 1 campaign to BoB is just uncanny and I think done on purpose. Similarly, COH 2 soviet campaign reminds me of enemy at the gates at first; and then switches too winter fall/downfall after 1943 in the SP missions.
Also explains a lot of over the top voice acting that you don't find in other games(people shouting all the time when in combat and such).