While I somewhat agree with you about some of this, the following undeniably proves that Luke 21:20-23 is pertaining to the first century leading up to 70 AD---and shall be led away captive into all nations(Luke 21:24).
Not correct, only a portion of what Jesus covered in Luke 21 involved events back in the 1st century A.D.
The not one stone atop another prophecy was also given in Christ's Olivet discourse of Matthew 24 and Mark 13. And the prophecy was never completely fulfilled. To this day there are still huge stones from the old temple complex standing in Jerusalem, called the Wailing Wall. And... the Muslim Dome of The Rock built with stones also is standing on the temple mount today. These FACTS signal only a PARTIAL FULFILLMENT of the not one stone atop another prophecy by Jesus.
But the devil and his servants definitely want... us to believe all of Christ's Olivet discourse Scripture has already been fulfilled back in 70 A.D., simply because that's a way to prevent Christ's servants from obeying His command for us to be 'watching' at the end of this world, as those SIGNS Jesus gave there are for the END of this world.
How does the 70 A.D. destruction of Jerusalem and the temple fit in though? The not one stone atop another prophecy serves as a DUAL FULFILLMENT type prophecy. And if you don't know how God's Word includes 'dual' prophetic events, then maybe you need more Old Testament Bible study.
The following Scripture is about the last day, the "day of the Lord" when the tribulation will be ended with Lord Jesus' coming...
Luke 21:20-22
20 And when ye shall see Jerusalem compassed with armies, then know that the desolation thereof is nigh.
21 Then let them which are in Judaea flee to the mountains; and let them which are in the midst of it depart out; and let not them that are in the countries enter thereinto.
22 For these be the days of vengeance, that all things which are written may be fulfilled.
KJV
"That all things which are written may be fulfilled"? That's definitely NOT about 70 A.D. That is about the very END of this world with Christ's future 2nd coming. At Lord Jesus' future return is when all things written regarding this present world, will be fulfilled.
In Luke 4 when Jesus began His Ministry, He read from the Book of Isaiah 61:1-2, but He closed the Book before He got to the Isaiah 61:2 phrase,
"... and the day of vengeance of our God; to comfort all that mourn;...". Reason He stopped and did not read that is because last phrase is for His future 2nd coming, His return.
And that... is what the timing of the above Luke 21:20-22 Scripture is about.