[Q]

I made the same observation: The AI is extremely cautious or reluctant to attack if he is not absolutely sure to win the combat. And this seems to be true no matter what mod you use. Even in the AI team setting, where I am the only enemy, mighty AI fleets that could wipe out my warp defences stay just forever motionsless without attacking.
A human player would sacrifice one fleet to destroy the defences and then come back with another fleet to attack the colonies.
That should be one important point to improve in SE V.