But i don't think that the AI of major factions does that. The game i'm playing now is much more easier than the game i played before which had no minor factions and the AI difficulty setting is the same.

I'm now also playing another 2v2v2 game with a friend in a team. When we research a new tech we trade it one to another and it gives us an advantage because the AI teams don't seem to do that.

actually i kind of like them for the flavor alone. galaxy feels more alive if there are some lesser powers screwing around but not really competing for victory. gameplay wise, they don't really serve much of a purpose and open some abusive strategies. i guess that's why they are set to "none" in the default settings? 

they could probably add some features to integrate them more in the game. for example, a mid-late diplo technology that allows you to absorb minors peacfully through diplomacy (a la star trek "federation").