I know all of the "cool kids" have moved on to Rebellion, but I find the lack of "Death Star, aka Titan" equivalents to be more challenging, so I'm still working at the Diplomacy level. And have been playing an interesting game, which I thought I could summarize and solicit comments/input on.
Started with 10 players in a 5-star universe. 5 players in one system, 5 in the other, 3 systems vacant. I chose to play this game with one AI player set on vicious, a few on cruel, and the rest on unfair.
Having watched on replay, I see that the Vicious player (now I can see he was TEC) appears to calculate the odds in his initial battles much more closely (attacking with less than maximum odds, but still winning in the end). Leading to faster colonization of the first few planets. Resources also appear to be less of a problem for building research facilities, frigates, etc. Everyone else, however, seems to match the human pace of expansion.
In the end, the Vicious player subdued two of the other players (one TEC, one Vasari) in his home system fairly quickly, colonized a second system, and then focused on two things. First, another player in his home system (Advent), and second, on financing pirate raids.
Fortunately for me, that Advent player was a particularly tough nut to crack, Which left the pirate raids to deal with.
Which were awe-inspiring. To this date (well, later in the game anyway) there are still stranded pirate fleets of 800+ ships sitting on several to many planets (please note that I know my grammar, and that is indeed "to" as opposed to "too". Since the vicious AI player and I focused on getting rid of the pirate homeworlds (I think that is only because I outbid him on a few auctions and the pirates attacked him instead of me), the pirates eventually stopped generating new raids. Mostly because of his Novalith bombardments, but also because I used my fleets to eliminate two pirate bases "the hard way". Which were challenging and took 4+ separate attacks to complete. At the same time I was expanding into the two other neutral systems using small fleets, but facing no opposition except for from native fleets.
It is later in the game now, and I have not only eliminated all threats in my three controlled systems, but I have moved into the enemy's home system and have begun absorbing neutral planets (mostly planets formerly owned by other dead players). In the face of which he has remained strangely passive. No recent attacks (in fact, none since the pirates died).
This leads me to believe that the AI is better in the short game than the long game. Others feel free to comment. This is a discussion thread, not an edict from Mt. Olympus. FWIW. YMMV. Etc.