As far as I can tell, in well over a 100 solo games in the last six months, there is not much wrong with artillery performance right now (in v 5.564 that I am using) except an "Artillery Corps" deployed in defence is not as powerful as it once was in the very early versions, and that is not a bad thing in my opinion. In the early days of HW we often had to wait until the artillery ran out of ammunition before it was safe to attack. It felt like WWW1 sometimes.
Right now I would say large scale attacks make an artillery corps easy to defeat, as most of the cannons will be lost, BUT, as JMM says, maybe that is because of not enough support close by. I like the way the attacking Corps attack a long line of cannons, looks just like I would expect it to. If positioned with the correct support, attacking those cannons would be much harder.
On the whole I would suggest not making any drastic changes just yet, if there is anything wrong now, it is by a very small degree, and probably comes under the heading of "player preference". Some would want more powerful cannons, others want less power..........so it could be called just right now !.