Over several games, I've noticed a pattern that seems pretty detrimental to the AI's effectiveness. AI fleets that are engaged against another player who then surrenders seem to become 'leaderless'. That is, they don't respond to higher-level threats that are outside of their immediate area.
In my current game at 'painful' difficulty, I am playing the Altarians in a 10-player, huge map game. Towards the end of the early game, my neighbours the Drengin declared war on their neighbours, the Drath. Naturally, I began building transports to invade the Drengin. As most of their fleet was fighting the Drath, it wasn't hard to take 3 of their planets in the first five turns of the war.
So far, so good. I can't really blame the AI, as it was fighting a 2-front war, and most of it's fleet was on the wrong front.
The Drengin took a couple of Drath planets, and the Drath surrendered to the humans. At this point, it's worth noting that the Drengin fleet was approximately twice the size of my fleet, and had a significant tech advantage. While I had been researching various 'butter' techs, they had been researching Lasers V, Logistics and lots of miniaturization. As a result, they had several fleets of 7-0 heavy fighters with 13 hitpoints at a time when the best ship I could build was 4-0 heavy fighters with 10 hitpoints. The vast majority of my fleet was 2-0 heavy fighters.
I move my fleets to the Drengin homeworld, and break my teeth on their defender fleets. They constructed an orbital fleet manager, and their defenders came in 5-0 size and 10-0 size. Orbiting Drengi, there were about 3 of each.
This is about the point where the killer Drengin fleets arrive back from nearby Drath space, and turn my remaining fleet into finely scattered particles for attacking their capital, right? Well, no. I guess those fleets were on shore leave, because they just sat in space while I picked off anything that tried to leave the orbit of the Drengin homeworld. Eventually I was able to construct a couple of enhanced fleets (the 4-0 type), get them all the way over there and basically swarm Drengi with heavy losses. It took about half a year to capture Drengi, and at any time those Drengin fleets over in the next sector could have swept in and kicked me out of their space. Kicked me halfway back to MY homeworld, if they were coordinated.
I've seen this many times. Attack fleets seem to get orphaned when their target surrenders. They don't do much of anything for a long time, regardless of how badly they might be needed elsewhere.
