From the early Middle Ages until the XIX century the Papacy was mostly held by members of a handful of noble families.
That's not entierly and neither systematically true : especially in the XIth and XIIIth centuries (but as well during Byzantine Papacy as well) you had an international drive to choose popes outside Roman politics, for political but as well ideological/theological reasons (such as bolstering the influence of new monastic movements).
It would be more correct to say that Papacy was an elected theocracy tempered by local and international politics.
Note that it's exactly why it couldn't lead to an hereditary title : it was far too disputed by local families and considered with great interest by the important kingdoms, that anyone would led a family litterally inheriting it : you had freaking schisms when French church tried to monopolize it in the XIVth, I don't dare to imagine if a given family would attempt this : you mention Borgias, and it's quite exemplary on how it finished on this matter.
As for Tusculani, they really get a bad rap, not totally undeserved,but mostly because Ottonian papacy needed someone to blame for the situation. In fact, Tusculani popes activrly augmented the power of the pontiff by feeding on their familial wealth and not the contrary. Even during Crescentii Papacy, most of the popes seem to have conflicted with the dominant family for the sake of at least a token independent institution. I think
@Carp know a lot about the Roman politics on this period, ang might be able to describe it better.