From my own experience with 4v4 maps, artillery pieces need to be kind-of counterable, otherwise they become unstoppable.
If you increase the cost disparity between single-click wipes and artillery pieces, that might be good enough. Like, if the map is so bad that you can't reach the enemy artillery, you could try counter-playing by capturing enough territory and hoarding munitions.
Requiring a team to spend 250MU to wipe a 400MP artillery piece would be what I would consider a fair trade.
An alternative would be to give arty pieces a short 5-second brace, at least to prevent single-click wipes, or make offmaps a bit less accurate, so that you don't have guaranteed wipes vs artillery (frustrating RNG though).
Yeah, I also thought about 5 second brace but I thought its too much of a copy paste and to easy to do for the owner of the gun. Still, anything that makes guns countered by 2 offmaps or offmap and follow up, instead of a single offmap is good and promotes team play.
I would also say that it would be better if guns, especially pak43 could be a little easier to destroy without using offmaps - so that it doesn't narrow doctrine choices that much.