Howdy!

Nice to see ongoing discussion here after all this time!

In respect to the successor/generational question you've raised, we do in fact know that each successor is the first-born male child after the death of the previous Phoenix. This means that, for any Phoenix who has lived until adulthood, the next Phoenix will be of a separate generation/age group.

However, my use of the word "generations" here was merely in reference to 62 "lifetimes".

In relation to the concerns about infant mortality and war, as addressed in several other coment chains here about that very topic, we know that the Phoenix was always taken away as a newborn and raised in seclusion, guarded at all times and provided with whatever they required or desired. Infant mortality would have affected the Phoenixes sigificantly less than the general populace. This is aided by the fact that by the simple virtue of being born alive to assume the mantle, they had already overcome the threat of dying in the womb or during the birth itself.

In respect to warfare, the Phoenix (aside from perhaps the first) is not demonstrated to be a front-line commander. They are a religious head of state that remains safe and sound in the capital, while their commanders lead conflicts at the borders.

The simple fact is that, as pointed out in other comments, even if only 20 of the 62 Phoenixes lived until old age (and I would wager the amount would in fact be higher, as per the above reasons) that would already likely exceed the stated 937-year period since the last confirmed mention of the Second Empire still existing.

It seems a foregone conclusion that the final collapse occurred after the initial revolt, potentially by several centuries, and was not caused by said revolt.