Hey,
After several tries I finally managed to get a huge galaxy with 9 hard AI going, me playing as TEC. Usually I would get ganged up on early by the AIs in my galaxy, fighting on 2-3 fronts and atleast 2 AIs were cooperating closely and coordinating their attacks perfectly.
This time however, I managed to stay afloat for more then 2 hours and got a solid foothold in the starting system. Having wiped out one AI and working on another, I have a solid chokepoint against the other 2 AIs in the system, who happen to be the best of buddies making large coordinated attacks on said chokepoint

For about 40 mins now they haven't made any moves, probably scared off the massive fleet I got defending it

Anyway, when I quit a short while ago I went through all the stats of the game (Awesome work with the charts and being able to pinpoint exact times and figures in it!). While doing so I noticed some obvious features of the game the AI was very bad at utilizing or plainly ignoring

Granted I've only played 3 hours so far, but they have all gotten quite far in the civic trees, where most of the flaws lie.
Mainly they are very bad at utilizing trade posts. They don't "play" the market, i.e setting their resources up for sale, instead of selling it directly. Now I realize that the market thing isnt a big deal and might be tricky to code a proper behaviour for, just thought I'd mention it

They never buy levels for their capitals, one AI was sitting on 15000 credits and still he never spent it on capital levels, of which most AIs had 4-6 of at this time.
There are many, many good and excellent things about the Sins AI, they colonize very aggressively and when they can't expand they tend to go to war quite soon. They do tend to leave their planets without many defensive structures, I don't think Ive seen even one hangar on their side, yet.
Anyway there's far too much info that might be useful to write it all down, so if Ironclad/SD are interested I'll gladly send the ongoing game to them if they want some info on how the hard AIs are faring in densely populated systems