From my limited play in USF - I didt find the mortars bad tbh , they do their job well.
Mortar half track ( doctrinal ) has been a fave of mine for awhile , scales quite well too till it gets pushed by Axis armour.
Pack howitzer I never use.. when I played axis I saw that thing as a wanna be LeiG and abit of a meme.
M8 is good , godly auto fire , barrage left alot to be desired.
Priest is good too , good range and splash. Probs best self propelled arty tbh.
Lets just vrush the calliope under the rug and not talk about it
Removing smoke from major strike would make it godly for wiping and be OP as hell. Anything off map needs marker , atleast give the sturmpio blob a chance.