Alexander VI died in 1503 which was fourteen years before Martin Luther did the 95 Theses; in 1503 Martin Luther was 20 years old, so he would remember a little of Alexander's papacy maybe. Depends on how much was known in Germany of the Borgia pope. It would be Julius II with which Martin Luther would be more familiar and with Leo X. Neither of those popes was noted for corruption. The assessment of Alexander VI by his successors is notable, Julius II said
I will not live in the same rooms as the Borgias lived. He [Alexander VI] desecrated the Holy Church as none before. He usurped the papal power by the devil's aid, and I forbid under the pain of excommunication anyone to speak or think of Borgia again. His name and memory must be forgotten. It must be crossed out of every document and memorial. His reign must be obliterated. All paintings made of the Borgias or for them must be covered over with black crepe. All the tombs of the Borgias must be opened and their bodies sent back to where they belong - to Spain.
And it is to be noted that the Borgia apartments remained sealed until nineteenth century.
Leo X was a Medici and consequently brought wealth and worldly power with him to the papal throne, no doubt his family's reputation would have an impact on perceptions about him, but the impact of his family was not wholly negative. It was Leo X who granted indulgences for financial contributions towards the payments for building the new Saint Peter's basilica in Rome and since it is generally thought that Martin Luther was most unhappy about the abuse of indulgences in his home land it seems to me that Leo X would be the main target of Martin's anti-papal comments and it was Leo X who issued the bulla excommunicating Martin Luther in 1521 (the name of the bulla is
Contra Errores).
Leo X responded to Luther's 95 theses with papal bulla
Exsurge Domine in June 1520. It was a case of too late and too little. By this time Luther's anti-papal movement was too widespread to stop. Luther had not been idle in the years since 1517 and his contempt for Leo X had not faltered so on 20th-December-1520 Martin Luther publicly burned a copy of
Exsurge Domine signifying his defiance and disdain for Leo X's authority.
The war of words was now so deeply entrenched that nothing on earth could heal it and we, who live almost five hundred years later, cannot heal it either. But for all of Martin Luther's rage against the pope it was the pandora's box that he opened that led to the most extensive and enduring divisions that we see today in the churches that came out of his protest.
