According to my numbers, artillery doesn't do nearly as much damage as infantry if both are deployed properly, and its inability to defend itself directly or to effectively remove itself from danger means it's pretty well dependent on infantry to protect it. It's all a moot point though, since we don't know how people end up engaging each other at closer or longer ranges yet.
Also it seems entrenching requires a unit to stand still for a day, and it'll presumably have to do it all again if it ever moves. Artillery is already slow, depending on how often artillery needs to be moved (probably a function of how mobile infantry units are in combat) entrenching them could be a kick from inconvenient to devastating.
According to my numbers, they deal fine. What I crunched suggested they will be able to take on the point value I assigned them in points. An entrenched LA artillery should be able to equal 7.5 militiamen per gun. Its a good deal less if it is out in the open v out in the open, but the only situation that would come up if we were retreating. Which is bad, but its not like having a bunch of infantry hugging it would help much anyway. Artillery is certainly less mobile, but it ain't like we are using it to take trenches.
The "Free shot" only applies to the Mass Charge action. What numbers are you running that suggests infantry can deal more damage unit per unit than arty?
*EDIT*
I also screwed up my math way back during my suggestion. We should probably just use Baffler's this round because I am too tired to fix it .*Open field LA v militia at 100 m*
> Assuming arty can't cautiously advance, and therefore always take 1/2 dice in damage. The militiamen are assumed to be moving cautiously, thus getting 1/3 dice in damage.
>> Each LA has a value of 7.5, each militiamen has a value of 1. Since artillery can't defend, the Militiamen get effectively double the attacks further doubling their damage to 1 dice/dice.
>>> Final: LA's have ~2.5 attack power compared to the Militiamen's one.
Thus LAs in the worst situation should be equal to 2.5 militiamen.
Entrenched militiamen are only worth 2 militiamen, so LAs in an open field are better equipped to deal with open field combat then militiamen are (aside from their not being nearly as many, of course.)