It's a tough one.
i remember when i first got the attacks i would get involved and help destroy the enemy.
..........so your natural reaction is to learn from the attacks and modify defences so that they are more effective.
I've finished the main game so now am doing things to make it more interesting til DLC comes out.
Presently I am not fast travelling so run and swim everywhere, just in plain clothes, that have no damage protection.
Swimming and running is consequently very fast.
I have suits of power armour scattered around the map in strategic locations, for those occassions they may be required.
So now when I am invited to help a settlement I might finish what i am doing then make a bee line for the settlement that is supposedly under attack.
Take last night, I'm in the middle of the map and respond to a callout by first running across country.
Past the stinging wasps and flies that chase me and give up.
Right between the two supermutants at Breakheart Banks who are standing side by side who say "What" and fire off a pot shot as i disappear into the night.
Past raiders too slow to keep up.
I cross rivers and reach the sea, diving in to take the shortcut to my destination at warwick farm.
After swimming for a couple of minutes I hear and see gunshots and missile fire in the distance.
As i approach shore the message flashes up.
Completed help defend the settlement.
i get to view another pile of bodies cut to pieces by my defences and loot yet another bag of missile launchers, other assorted weaponry and armour pieces.
Perhaps it would have been better to not have installed those missile turrets and walled defences, as i might still be able to join in.
Not wearing armour makes me highly susceptible to friendly fire but it's all over before I get there anyway.
I don't know how they could change it.
They would have to stop issuing callouts so what would be the point of putting in defences.
Also from previous experience if they initiate an attack while you are at a settlement but for whatever reason you leave just before the commotion starts, it's an instant fail because the game registers that you have failed to provide assistance.
So perhaps they should issue written advice of an imminent settlement attack even if you are there at the time.
Another possibility is that they only instigate attacks on settlements that are within a shortish distance from your present location.
I suppose the trouble with that is those who don't get out much will get the same settlement repeatedly attacked.