I have an issue with the fast firing arty, like mortars and the self propelled versions, the 10-15 shots/min ones, simply because they are incredibly accurate. Even blind firing they are more accurate than tanks or AT guns, most of the time. Yes, I know it's because of the blast radius but I think it removes quite a bit of the threat factor of AT guns as they are dead 10 sec after being revealed.
Stuff like the off map arty, Nebelwerfers, Xylophones, Callilopes I have no issue with as they fire once then have downtime. It's the continous, highly accurate fire from, especially phase A, mortar teams and self propelled mortars.