I read your post in the British Commander Revamp thread and agree with most of what you said.
However, the Sexton was inferior in every way to the Priest. The 25 pdr is only an ~89mm gun; the Priest had a 105 (I don't know why the British preferred the Sexton). You want to make it like a 120 mm mortar but, that's just unrealistic. The developers do need to fix the rate of fire, the accuracy, and the costs but, the damage is pretty consistent with a gun of that calibre. It's way closer to a 75 than a 120. The closest comparable gun is the German 88; unfortunately, there isn't an 88 in the game that fires in indirect mode.
I posted this here because the thread is for new ideas, not discussions about historical accuracy. I hope you don't mind. Cheers.