the terra is well known, the ai just doesn't know that it exists as a concept. The reason behind that is plain, the AI was written by someone and wth terraforming you can change the entire map. Consider the possibilities aside of just making walls to keep units out. Sadly, all that crazy amount of possibilities is very hard to put into a solid tactic. Youw ill notice that even human players don't make much creative use of terraforming, you will be lucky to see someone remember to wall off their mexes to protect them from raiders.
As for porc yes, that is likely due how the AI calculates dangers. It will ocasionally send careful probing attacks (those tiny groups) to see what danger is where and based on that, if i recall correclty, makes a map with how scary what area is. And not carelessly attack unless it is quite confident it can win.
Which totally leads it to being very deterent by a stinger. But mind that also means that it won't waste units to break through a stronghold when i can find an area you forgot to fortify. Which is pretty good.
Lastly... consider other games where the ai will mindlessly throw waves of fix size at your defenses, turning it into tower defense in the end. It certainly would be good if someone can teach our ai how do to sieges, but considering the very effective artillery options you have and ais endless micro, it might be very terrifying if it finds out that a single sling can reliable murder your porc and then just sieges you on the entire map, ready to swipe through your backline with a few glaives ;-;
