Don't really know why you call it nerf. The faction would remain exactly the same.
Can you develop?
If you have a car factory and except performing repairs I won't let you do anything else aka produce cars, would this be a nerf to your business?
What you propose will result in cutting okw's any initiative because it will hug the trucks all game in order to avoid decaping. If we think at partisans, paras, and other units that can just be dropped in, things are getting even worst. Let's say you successfuly do an attack and, because your OPness of you okw units (
) - not skill, God Forbid
- you drove you opponent back. Then, instead capping your deserved teritorry, you will have to retreat to your truck just because your "skillfull" wonder-opponent who just lost the engagement, will drop a Paras unit near your T2 truck and decap point. Or will spawn a partisan unit to do the same thing. If there is a T2, then your retreat attempt may work. If it's T3, it's bye bye.
Building defenses around every field deployed truck? No thanks.
What you want in fact is OKW building its tiers inside base. No thanks again. Deploying trucks on the field is one of the features that makes OKW interesting.
Don't forget that british trucks had some other features
related to resources and teritorry securing that balanced things. OKW trucks have no such features. They are just buildings deployed outside base, except for T4 which is a stronghold.