And, I'll repeat again, people beating it at the highest level are usually playing against an outright hole in the AI logic. I'd love to see someone simply explain, step by step, how they win at those high levels.
Not sure what you mean with highest level. But I usually play on painful or tough and depending on my start position it's generally no problem to win. If the AI gets way ahead of my technologically, economically etc then I will lose but that has more to do with strength in numbers rather than tactical brilliance.
I dont remember using a step by step strategy to win but its rather has to do with the AI not taking advantage of situations as I do. For example, there has been many times where the AI was way ahead of my militarily (maybe twice or three times my military rating) but all it did was demand tribute of me, which I gladly paid, and then when I was ready I just rolled them over. If it was smart it would have killed me of when he had the chance.
I imagine this has something to do with diplomacy as it has huge effects on the AI but little to no effect on human players and I almost always go for high diplomacy since I know what huge advantage this will get me. It shouldnt be like this, if it sees a weakness it should go for the throat. Just as any decent human player would do.
Also the AI is very poor at managing his fleets. It cannot use basic defensive tactics, doesnt seem to have a concept of holding a defensive line but rather just puts a bunch of ships into orbit without orbital fleet management.
Furthermore its attacks arent very coordinated. It seems to just sends a bunch of ships towards you in waves, rather than to do it in a big coordinated attack. It should amass one or two huge fleets and then send it at a few locations, backed up with transports. Also it should put alot more focus on destroying resource starbases as it is usually a big blow to lose one.
Finally it is too slow to react in regards to ship design. Often when I start planning for designing ships I poll other empires around me and see what attack and defence they are focusing on and then I focus my research and design on areas which they are weak to. For some strange reason most AIs seem to focus in the same areas, even with tech trading of, which have my ships designed to be strong against most of the AI empires.
Im not sure how this works but the AI should poll other empires ship setups more often and then design it ships to be strong at those empires most likely to be a threat. Also it should do this continually and adapt to new threats, not sure if it does this already but I rarely see an AI adapt to me changing my ship setups.