I started playing around 1.05 and I can tell you the CB was in the game as early as that.I've played several Southern Italy games and I've never had the problem before, so I assumed the CB was new. Even if it's not new, something has changed for the worse. In earlier versions the Merchant Republics would only take land in Southern Italy when they reconquered it from Muslims via holy war.
No. In my last attempt at the County of Naples I wasn't actually attacked by Genoa, but they happily ate the entirety of Apulia around me. I was allied to the Normans and there was nothing we could do.
Could those saying you like the CB actually express why you like it? I don't see any redeeming qualities at the moment. This CB is supposed to be used by Merchants Republics to beat up on the Byzantines, not to allow them to go on a Muslim-esque conquest spree in Southern Italy.
Genoa's conquest of de jure Sicily is dependent on 1 thing: holy wars. If Apulia/Kingdom of Sicily are under attack from muslims Genoa won't attack and vassals won't rebel giving Genoa opportunities to expand.
I like the CB because it makes the game more interesting, back in 1.06 the county of Ormond was controlled by a norwegian mayor who tended to rebel against the duke of Munster(the rebellion hasn't changed even though Ormond is now a boring lordship). If Ormond won it's independence it was like watching a zombie outbreak in action, first it would begin eating up neighboring irish counties, then it would strike any independent welshmen or the remains of the duchy of the Isles. Soon the merchant empire would be attacking Brittany and larger kingdoms in the middle of civil wars. I once played a game in Iberia where I didn't notice anything wrong until Navarra lost its capitol, then I looked at the rest of the world and saw that France had lost it's northern coast, the scandinavian kingdoms were being pushed back into Finland, and even the HRE was losing beach-side property.
Nothing is better for a game you spend hundreds of hours playing than for things to be able to go that crazy.