Call it tactics or an exploit, but currently the best way to counter AI assaults is to build a walled-in colony with just one entrance and post a bunch of turrets in close view of this entrance inside the walls. Whenever the AI attacks, you just wait for the attackers to beeline for the one entrance and be mowed down by the turrets when they break down the autodoor.
This means the game loses its challenge, since there's not a whole lot of other stuff to worry about once the base really gets going.
I suggest the following solutions:
More expensive turrets
Easiest solution. Turrets are efficient, cheap and easy to build en masse. Make them more expensive or less useful.
Blackout device
Moderately easy solution. Technologically advanced AI factions might use a blackout device that works like a solar flare (but shorter duration) when assaulting. This would make depending on turrets a risky strategy.
Destroy the base
Instead of going for just pawns and turrets, the AI targets all structures in the colony in the vicinity of pawns and turrets. This means it would try to break down walls that would otherwise funnel the AI assault force into the free-fire zone on the other side of the entrance. Perhaps difficult to program.
Hole-in-wall approach (or 'the Kool-Aid')
(in conjunction with above tactic) The AI has something dedicated to making holes in the walls. A single shot grenade or rocket launcher would do the trick, or perhaps explosives, C4 style, with dedicated AI.
Sappers
The above would not work that well if the player is using a hollowed-out mountain as base. How about the AI setting up base close to the player colony, but on the other side of the mountain, and then it starts tunneling into the mountain toward the player?
Besiege the entrance
If the player has the single-entrance setup, the AI sets up a base just outside that entrance and waits out the player, who is pretty much forced to sally out.
Fog-of-war
Finally, the game really should have a fog-of-war, like so many other games. This would make the AI generally and mortar sieges in particular harder to counter. You would need scouts to find the enemy and direct your artillery fire, and perhaps you would not be warned about AI assaults before you actually see them...
This means the game loses its challenge, since there's not a whole lot of other stuff to worry about once the base really gets going.
I suggest the following solutions:
More expensive turrets
Easiest solution. Turrets are efficient, cheap and easy to build en masse. Make them more expensive or less useful.
Blackout device
Moderately easy solution. Technologically advanced AI factions might use a blackout device that works like a solar flare (but shorter duration) when assaulting. This would make depending on turrets a risky strategy.
Destroy the base
Instead of going for just pawns and turrets, the AI targets all structures in the colony in the vicinity of pawns and turrets. This means it would try to break down walls that would otherwise funnel the AI assault force into the free-fire zone on the other side of the entrance. Perhaps difficult to program.
Hole-in-wall approach (or 'the Kool-Aid')
(in conjunction with above tactic) The AI has something dedicated to making holes in the walls. A single shot grenade or rocket launcher would do the trick, or perhaps explosives, C4 style, with dedicated AI.
Sappers
The above would not work that well if the player is using a hollowed-out mountain as base. How about the AI setting up base close to the player colony, but on the other side of the mountain, and then it starts tunneling into the mountain toward the player?
Besiege the entrance
If the player has the single-entrance setup, the AI sets up a base just outside that entrance and waits out the player, who is pretty much forced to sally out.
Fog-of-war
Finally, the game really should have a fog-of-war, like so many other games. This would make the AI generally and mortar sieges in particular harder to counter. You would need scouts to find the enemy and direct your artillery fire, and perhaps you would not be warned about AI assaults before you actually see them...