Well actually you highlight some more than fair arguments, but I think you lose sight of the important details, for the development of the situation, first of all let's address what Cesare's real priorities are at this moment: the first obviously is to try to obtain a ' pontiff friend of him, is considering that Cesare inherited his father's immense patronage network ( also it must be considered that Rodrigo in his decades as vice-chancellor ( only as vice-chancellor, Rodrigo obtained a figure amounting to 60 thousand ducats, to which must be added other extra earnings from the various secondary positions obtained over time ) had meticulously set aside a substantial financial reserve to support his family ambitions, this little treasure, which is completely foreign to the papal treasury, can become an important resource for Cesare in the future, especially if it is added to the annual income he obtains as head of the papal army ( a sum that varies around 15/10 thousand ducats ), to which his ability to influence must also be added in the curia, thanks to his role as papal standard-bearer and the ties he personally built in the Roman aristocracy, the chances of getting a Pope, who comes from the pro-Borgia faction in the curia, are quite good ( Pius III himself was his creation ) this would be his main purpose, for an obvious reason, to have the titles created by his father recognized and approved by a second pontiff, so as to consolidate his position in Romagna, his other priority is to try to obtain imperial recognition for his possessions, so as to make his eventual deposition legally impossible, without a cause recognized as legitimately valid at an international level, this fact alone, practically read any French / Spanish ambition of being able to play a bad joke on them, at most one could try to support a rival candidate for his dominions or a part of them ( in particular this can be seen purely as an anti-Louis XII function, given that Paris might want to support Caterina Sforza and her children , who have local claims, but who have a serious obstacle to this, namely that the people of Romagna have made it clear that rather than having a Riario - Sforza government again, they would prefer to go to hell, therefore Cesare would be even more supported at the level local, if that were the alternative ) also because Paris cannot afford to depose or annex an Italian state, not openly hostile to it, given that it would nullify its laborious policy with the local potentates, carried out with the aim of further legitimizing its presence and government in the region, but making a such a maneuver ( deposing and then annexing the Borgia dominions ) would create the opposite effect, given that the vast majority of the Italian potentates would immediately rush into the arms of Spain, seeking protection, thus making it even more precarious and compromising the any possibility of recognition of the French presence on the peninsula, therefore it is more likely that Cesare will end up being courted by the two factions fighting for the domination of Italy, given his important strategic position, but I am convinced that if he manages to overcome the first 10/15 years of reign in his new duchy, the chances of him being deposed begin to progressively decrease, until the unanimous recognition that that territory is a dynastic possession of the Borgia family
without forgetting that nepotism will certainly still exist, and it was not an exclusive prerogative of the Italians ( Hadrian VI himself tried to fill his government with relatives and friends, in order to strengthen his position in Rome ) but of places where it could be practiced in peninsula there are plenty of them ( just think of Lunigiana and western Emilia, which were regions full of tiny local fiefdoms, which could be very suitable for an attempt to install a relative of the current Pope, for example Innocent VIII, successfully obtains a dynastic fiefdom for his nephew, in the region ) furthermore depending on the precise moment in which the Pod takes place, it could happen that Rodrigo's death itself is postponed for some time, drastically changing the cards on the table
P.s
in case Cesare needs a second wife, I personally would opt for Bianca Riario, so as to reduce the threat of the dynastic claims of the tiger of Forlì and family, in the region, while looking for an important match on an international level for his firstborn