The Borgias were a symptom. It was a time of tons of infighting among the Italian states, and against the Holy Roman Empire up north. There was tons of Italian wealth from trading, a new amount of free time, and people who had survived the Black Death were able to inherit or claim a lot of abandoned money and land. There were also tons of mercenary armies roaming around, selling their services to the highest bidder.
So yeah, the Borgias were up to no good, just like a lot of the other noble or rich Italian families. But we hear more historical rumors about them, because they were more conspicuously successful in a short time, and because they originally came from Spain. But yeah, Pope Alexander VI seems to have done a decent job as pope, on the business side, even if there were serious problems on the morals and nepotism side. All the poisoning stories seem to be the same level of believability as aliens and Bat-Boy visitiing the White House.
But… it’s hard to tell. We weren’t there with a forensics investigation team. There was a lot of poisoning in the Italian Renaissance, but there was also a lot of disease, and a lot of doctors prescribing poisonous substances. Women used arsenic, lead, and mercury as makeup.
Either way, the same family produced St. Francis Borgia, who was a model of morality and good judgment, and who gave up everything to serve the Lord. So it was an interesting family altogether.