beware of the anti bias player ai_threat_score_personality_multiplier_player

you've set to 0, 0.25 and 0,75

meaning on easy the AI will ignore the player and legendary player will be 25% less threatening than AI .

From description :

(In-game) An additional value that the players threat score is multiplied by (effectively set at 1 when calculating for all non player factions threat scores) in common threat in diplomacy calculations. The calculation for overall threat is base_score * attitude_multiplier * direct_actions_mulitplier * proximity_multiplier * personality_multiplier_player. This means setting any multiplier to zero will lead to threat being zero.