One minor issue here on the economics part. Quoting Quietus's economic guide (https://forums.totalwar.org/vb/showthread.php?t=40072):

"Highways: 50% land trade boost from Paved Road in originating city only. In my test, only 3 of 5 got the increase, the two lowest values didn’t increase. There maybe a) a distance limit how far a highway upgrade is effective (the two farthers didn’t get a boost) or b) only a fraction of the land trades get a boost (3 of the 5 were the highest values). Neither sea exports nor imports were affected by the upgrade. Currently, I’m leaning towards choice a)."


I made 1 check BEFORE patch 1.2 and it seemed to be true. IIRC, 3 out of 5 possible provinces adjacent to Patavium got the boost. Rather risky to make conclusions based on 1 observation though.
However since Quietus and I have essentially observed the same odd phenomenon, I would think that it is worth looking into. They might have 'corrected' it for the patch or perhaps it's still the way it is.