Arty always seemed worse to me. Once you discover the power of arty you pretty much have to turn up the difficulty until the AI will beat you to, or match your time to, arty, or games are trivial, and it has to be every AI that matches your time or you just snack on a free lunch at the arty spike and consolidate your new empire.
For example, last night I played on emperor. I had a horrible start being pinched between three empires. Really should have been a lost game, but the koreans on one side were being slow to arty as they were even a little bit worse off than me. My neighbor on the other side were way ahead of all of us and had taken most of the continent. I had a war with Koreans. Hit an arty spike. Stomped their entire side quickly, and then turned to my other neighbor who got arty just a tad after me (he had gone flight), but the point is I now had a decent sized empire because of the arty spike and I could deal with them by targeting down their arty. Strategically lost game--won by arty.
In an Arty versus non-arty war, neighboring AIs pretty much just have to give you their entire empire. It is by far the biggest bump in in city taking power in the game and the hardest for the AI to deal with. Also, if for some reason you had the sense to make horse units that got the promotion to see 3 squares this applies double because you no longer have the "I can't see the city problem."
Now, if the AI has arty and you have arty it is bad but not as bad for the AI, so it is a bit of a design flaw and an AI flaw.