Christianity of course was established at Pentecost 50 days after Jesus was in heaven.
Yes, Luke chapter 21 took place well after Pentecost when the Roman armies came in the year 70.
Luke wrote that Satan showed (offered) Jesus all the world's governments at Luke 4:5 that is more than Rome.
Luke...
ActsoftheApostles 17:6, ActsoftheApostles24:5, ActsoftheApostles 28:22
Of course it doesn't matter whether I believe it was fulfilled - the question is whether the writer ofthe prophecy thought it had been.