Yes Wehrmacht have a lot of artillery variety. But this arty is less accessible than allied arty. Brit 25lbers, while needing a buff are non-doctrinal and since most Brits go arty doctrine, Priests may as well be. The majority of American players go infantry who makes use of an excellent howitzer and also a call-in ability that is extremely useful in most situations (they also float quite a bit of munis, unlike wehr). Armour doctrine, who pretty much is always RHS first, gets the best artillery in the game in calliopes.
Wehr has to spend many munitions on their units and can use less call-in strikes as a result. Stukas are also very expensive in a 1v1 and nebels are T3 only and very vulnerable to counter arty. Officers are very rarely used as well.
I'm not trying to justify wehr having an AT gun that can cloak, as I've already said it's a stupid idea. However, this is the way I believe Relic justifies it, as well as Wehrmacht being defensively oriented and this fits in with that idea.
PS. The correct term is faction not "fraction".
If you get into an argument with me, you're wrong.