Defensive Artillery

Right.

With a shorter recalibration time your alliance's artillery is a factor in pvp.

 With a longer calibration one attacking base can do significant damage if the defending alliance has no members online since defense artillery is not a factor until after the first attack maybe even the second. 

Spitting then alternating your attacks between multiple targets can be used to fool the lagging defensive artillery into wasting recalibration time on the wrong base.

Attacking a base alone with 10 or 15 allied artillery in range should be more costly than it is now.

A minute and a half to two minutes would be a good compromise. 

Two minutes will give a good defense time to react by the second attack.

Artillery in my opinion should be offensive too.

Maybe being able attack specific enemy buildings?

Not the point though.... 😞

 Yes.

Like the Ion Cannon from the old c and c.

And yes focused artillery during an attack would be great.

But in my opinion if you have never seen defense artillery stop an attack from a superior force which didn't commit enough resources to the effort then being forced to maneuver defensively.....

You just haven't seen it at all. 😎

With robust artillery smaller alliances with lower levels will be much less likely to be successful if they decided to attack.

So their diplomacy must be on a higher level.