You are right,yet the Katyusha seems to be only one who is currently not overperforming in that case... perhaps even a little bit underperforming.
Katusha and stuka are the only mobile arty vehicle's that are fine atm.
Werfer is too good but also too hard to get, fix in both those area's is needed.
Caliope is pure insanity (durability of a medium tank+wipe potential of werfer, just lovely)
Sexton and priest, well i generally am laughing too hard to notice their performance