That's where the circularity comes in. The argument assumes the conclusion. The conclusion: the events didn't happen in 70 AD. The premise: the events didn't happen in 70 AD. The very definition of circular reasoning.
How would the argument be made legitimate? By demonstrating that the events didn't occur in 70 AD. Asserting, however, is not the same as demonstrating.
No historian records the events of "A" ... period.
If you assume (and you ARE assuming it) that the events in Matt 24 are past events, then Daniel and Revelation, the minor prophets, Psalms ... just about every prophecy has been fulfilled.
Can you point me to a historian who records when Jesus Christ came in the clouds of heaven? Don't see any mention of stars falling from the sky, or the Son of Man coming in the clouds of heaven in Josephus. Don't recall Josephus reminding us that after the coming in the clouds Jesus received the earthly kingdom, and all nations then started serving Him. Seems like to this day you wont find anyone in Saudi Arabia serving him ... wouldnt you see that as a clear violation of "all nations" ...
Since all the tribes will have morned when they saw him in 70 AD, its probably a double good idea to have a couple of historians in different parts of the world ... since this is a global event for everyone to see.
Good luck with that ...