what effect do the stars a general have do to the units?

i fought against genearls with 7 stars with me only having a 1 star general or only a captain and won those battles easy. the enemy routed quick, even troops with high morale have routed quick.

on the other hand i fought peasants with high morale with sassanids cavalry and lost. it was like running into a brickwall.

in MTW i could hardly win against a 8 star general with a 4 star general.