Machiavelli is saying the opposite of what you think he's saying.
He's saying that France's governmental structure makes it (relatively) easy to conquer. Because there are many quasi-independent, competing fiefs, an invader is not necessarily facing a unified front, and may in fact be able to recruit dissatisfied lords to their cause. But that doesn't make it the kind of place you'd want to rule, because once you've conquered it, it's (relatively) easy for another invader to conquer you for the same reasons.
In contrast, there were no fiefdoms in Persia. Unlike the lords in France, the regional rulers in Persia were chosen by the state, and picked for their loyalty. When invading Persia, you are far more likely to face a united front, making it (relatively) difficult to conquer. That said, once you've conquered it, it would be (relatively) easy to hold for the same reasons.
Otherwise, we are saying the same thing.
In some cases the old king of the conquered kingdom depended on his lords. 16th century France, or in other words France as it was at the time of writing of The Prince, is given by Machiavelli as an example of such a kingdom. These are easy to enter but difficult to hold.
When the kingdom revolves around the king, with everyone else his servant, then it is difficult to enter but easy to hold. The solution is to eliminate the old bloodline of the prince. Machiavelli used the Persian empire of Darius III, conquered by Alexander the Great, to illustrate this point and then noted that the Medici, if they think about it, will find this historical example similar to the "kingdom of the Turk" (Ottoman Empire) in their time – making this a potentially easier conquest to hold than France would be.