War thunder has several spa vehicles, though the are labeled tank destroyers, I would love to see then being used as spa vehicles and here is one possible way to do that without making them too powerful:
In arcade battles spa vehicles could have a second map that shows the approximate location of where the projectile would hit the ground but things like trees and other obstructions (not including buildings) would not show up giving the players target a better chance of survival and only the targets last “marked” location can be seen not the target itself. The marker can only be set by the player or a squad mate if they are in a light vehicle (with some other exceptions).
In realistic and simulator battles they do not have that oh so useful map but they still have the markers with the same restrictions.
I would suggest adding better sights for spa vehicles for better accuracy as an optional sight.
Oh you can also add in wind and basic weather conditions like rain reducing the distance and so on for simulator battles with later vehicles having indicators displaying the additional information and another horizontal line because of the wind curving the trajectory of the projectile.
Maybe put that last one in as an additional option or a test run to see how players react.