I've found the AI's expansion is strongly tied to the map. In ancient quadrants, the AI is lucky to get 4 systems. In grids they expand very rapidly. Galactic edge slows them down a bit less than ancient quadrants.
Someone else (forgive my bad memory) posted that he found a high number of AIs and neutrals makes them all weaker. I'd only just been discovering that myself. When there are a lot of them, they get into multi-front wars and can never use their fleets intelligently. Against just one enemy, they fight quite a bit better.
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