Yeah I played again the scenario. Now at "tribune" ai ranking. It was a crazy ride. The ai was really good at these difficult. I went straight to their capital, after initial nearby cities. They held fiercely their capital. They had almost 80 thousand infantry. One thing to note is that they didn't entered the city, they stood there to defend in the region. Very good movie by the ai.
In the end, I achieve to obtain all their victory objectives (cities), and this time I took care to "garrison" the cities with regular units. The major victory didn't came, and I had a minor defeat by Victory Points by 36 points
Their morale was very high even on the end of the scenario that I hit them completely.
I could have won by VP, but I lost two precious legions on the sea (very coll how seas storm is a dangerous thing to care), that could have speed up the capture of their cities.
Well, nonetheless I am happy with the campaign by the end. I was able to conquer all their victory objectives, and annihilated their army (they had almost 100 thousand deaths more than mine).