Although the Panzerwerfer can (arguably) be considered the Ostheer/Wehrmacht equivalent of the "Walking Stuka" (in terms of selecting an artillery piece), the roles that each one fulfills (respectively) greatly vary. The Oberkommando West's "Walking Stuka" is more-or-less designed to hard-counter garrisoned units in buildings, static positions (mounted team weapons and immobile artillery pieces), and to a lesser extent blobs – while as the Panzerwerfer for the Wehrmacht is designed to directly provide a hard-counter Allied blobbing of units. Just because the Panzerwerfer isn't as "spot on" in wrecking enemy units, doesn't mean it is "less-efficient" (in lack of a better phrase) as a unit. It simply just means that they are designated to perform different tasks when a player utilizes them in combat.
I totally agree, However when the Panzerwerfer is compared to its direct counterpart (The kat truck) it is painfully obvious that the kat truck is simply just better at its job.
Kat truck can fire and hit units that hit T as soon as they hear the sound and catch units.
While the Panzerwerfer can fire on a immobile blob and kill 3 models. If it was a kat truck it would wipe most of those units.
Stuka is what panzerwefer wishes it can be when it grows up.
(Please note that I don't want the Panzerwefer to be better then Kat, those two units need to be equal is all)