Artis are generally a complete and utter waste of shields in multiplayer. Most big battles only last 1-2 turns making the artis rather useless. Assuming you are not playing against total newbs or have certain map advantages, such as chokepoints. The only time I would actually consider building artis of any kind is if the enemy is sitting on mountains/hills and won't come down. What works great in SP does not necessary work great in MP!
Perhaps they are. I am not that experienced in multi.player.
My comment was made in the light of how bombers are nullified by bringing mobile sams with a stack. When a force has attacked us and tried to take our cities, we could counterattack and pick off their injured attackers with bombers and MA.
But since bombers are now nullified, I was thinking maybe a stack of arty could soften them up before picking them off. Not that I expect us to get many units to kill anyway....but it was just a thought.
but when you look at the actual cost you realize that you might aswell get units. In SP the AI never brings full force and you can easily pick him off every turn, but in MP the other players are gonna bring every available unit they have to tip the scale their way, and thus creating a situation where artis do very little in the big picture, as the battle is over before the artis have fired their 2nd shot.

I even posted a pic of that event.
- I'm just glad I wasn't losing my mind!