If I understand well, Mark has a problem: the temple's destruction is not contemplated in the original prophecies pre-70 or, if it was, had to be the work of the Superman Jesus, not of the Romans. In both the cases: contradiction.When the temple was destroyed, the Christians took this as a sign that their imminence predictions were coming to pass. But was the temple's destruction specifically part of the original prophecy? Maybe, maybe not. Mark seems to be trying to square that - trying to include the temple's destruction into the "this generation" prophecies that predate him.
From this point of view, what Mark is doing is a pure apology, not an allegory 'of the destruction of temple'.
But what if the destruction of the temple was simply the visible sign of failure of the god of Jews?
So Judith M. Lieu:
Mark would have a precise theological interest in 'trying to include the temple's destruction into the "this generation" prophecies that predate him' because only in this way he can give a solution for the marcionite antithesis ('the Messiah is came but the end didn't arrive').The effect of such omissions would be for the crucifixion to be marked
primarily by the dramatic darkness; for Tertullian this makes no sense –
surely creation should rejoice at the death of the opponent of the Creator –
but Marcion could no doubt offer a more congenial interpretation, perhaps
that it was a sign of the defeat of the Creator’s powers. Unlike Epiphanius,
Tertullian also refers to the splitting of the Temple veil, caused, he says, by
the violent exit of the angel deserting ‘the daughter of Zion’ (AM IV. 42.5).
It is uncertain whether this represents his own interpretation or something
that was in the text before him; such a tradition is found in a variety of forms
in the second and third century, in some cases signifying the departure of
God’s presence or spirit from the Temple. This takes a distinctive form in
Eznik of Kolb’s account of Marcion, where the Creator darkens the sun and
tears ‘his robe and the curtain of his Temple’ in anger at the trick played on
him (De Deo 358)
(Marcion and the Making of a Heretic, p.217-218, my bold)
But if this is the case, why marcionites put Jesus in 30 CE?
A possible solution I would re-value is the known cruelty of Pilate.
As story goes in Mcn:
1) Pilate finds Jesus innocent, at contrary of the Jews.
2) the 'Just' Creator, only by his permitting indifferently the crucifixion of Jesus the Innocent, becomes unjust according to his own law.
3) therefore the Creator becomes more unjust than - and therefore more guilty - the same Pilate (who is a known war criminal). The message is: after the crucifixion of the Son, the Creator is really more cruel than the worst of the Romans.