Many miracle stories might be dismissed as "allegory" only -- but the Jesus miracle acts must have been real historical events.
Causes of the Temple's Destruction at josephus.org -- "Why the Almighty Caused Jerusalem and His Temple to be Destroyed". That page has a whole section on "Omens of Destruction" (War of the Jews 6.5.3 288-309):
- Star and Comet -- Thus there was a star resembling a sword, which stood over the city, and a comet, that continued a whole year.
- Light Around the Altar -- ... at the ninth hour of the night, so great a light shone round the altar and the holy house, that it appeared to be bright day time; which lasted for half an hour.
- Cow Gives Birth to Lamb
- The Eastern Gate -- of the inner temple ... (though it was very heavy, it) was seen to be opened of its own accord about the sixth hour of the night.
- Miraculous Phenomenon of Chariots in the Air ... before sun-setting, chariots and troops of soldiers in their armor were seen running about among the clouds, and surrounding of cities.
- Weird voices
(On Josephus's omens of the conquest of Jerusalem)
You are right to place this directly after your Asimov quote, as portents like these are to be taken mostly as metaphor. Such symbolic language is frequent in connection with battle scenes, where signs in the sky are described, or other weird happenings, which are supposed to be announcing that the gods favor one side or the other.
What gives you that idea? Why would those miracles be allegorical and not (say) Jesus Christ's miracles?
simple answer: The Jesus miracles in the gospels are best explained as real events, for which we have the same kind of evidence as we have for normal historical events. Whereas these Josephus visions are best explained as fiction, similar to other "miracle" scenes in writings which describe a battle scene, and for which there is virtually no evidence as being literal historical happenings, because they appear in one source only and it's easy to identify the writer's motivation, promoting an idea or a theory about the gods and their involvement with certain earthly characters and nations or tribes, etc.
But there's another way to explain why the Jesus miracle stories cannot be taken as allegory and were not so intended by the writers.
If the literal meaning is essential to the writer's message, then the meaning must be literal and not allegorical.
The above Josephus excerpt, listing the portents or "signs from God" at this Jerusalem scene, are only decoration being added to his account of the mayhem taking place. He could have omitted this from his description without doing harm to his account, because the purpose of his work is served by presenting us with these events, minus the "miracle" visions, so we can have knowledge of what happened and how history unfolded at this time for the Jews, and especially how this event changed the course of history for them, with their temple being destroyed and the people suffering such a setback and becoming scattered.
We don't need these visions Josephus presents in order to get this picture of what happened, even if they add extra sensationalism to the scene. He could easily have left this "miracle" element out and we would still see clearly the course of events and understand the essence of what happened.
But this cannot be said regarding the miracles of Jesus in the gospel accounts.
The "GOSPEL" of Christ has no substance without the miracle acts.
If the Jesus miracle acts are omitted, what's left remaining is incomplete and doesn't makes sense.
What is the "gospel" if Jesus did not have power such as described in these miracle healing acts? What is the "good news" if he had no power? if he was just another ordinary human with no special power?
The demonstration of his power, especially his resurrection and thus overcoming of death, and the realization that he had/has this power, is what makes Jesus important in history and explains why he attracted "disciples" and became the object of the gospel writings and the Paul epistles. If he had not demonstrated this power, in physical observable acts, he would have been a nobody and would not have been worshiped by anyone or written about.
What would there have been to write about? Without that power he demonstrated, he would have been just one more failed messiah pretender, one more babbling preacher among hundreds (or thousands) who were ignored and entirely forgotten (or 99% forgotten in a few cases where a charismatic did get enough notice to be mentioned once or twice in the written record 100-200 years later).
So a major difference between the Jesus "miracle" stories and others, like this example in Josephus, is that the writings about Jesus could never have happened if those miracle events described had not taken place (or if no one had believed they took place), whereas the Josephus writings would certainly have happened anyway, and would have served the purpose, without those "signs" in the sky, etc. being included.
The basic message of the gospel accounts, or the basic mission of Jesus, could not exist or have any substance without the mention of the power he demonstrated as being at the center of it, whereas it should be clear to anyone that the stories of portents or signs in the sky at these battle scenes -- in Josephus, Herodotus, and others -- do not add anything of substance to those accounts, except as a kind of "icing on the cake" at most, and could easily have been excluded without omitting anything essential.