I'm one who thinks that Pius XII did do it, but too late and imperfectly, ...
I totally disagree. He didn't do it. And the fact that he shorted Our Lady was almost an insult to her.
Pius XII did nothing but preside over the destruction of the Church. He's responsible for Vatican II more than any other single individual (apart from Satan himself).
Not only did he fail to avert it by making a very simple act of consecration, but he ...
1) installed, during his lengthy reign, nearly every bishop that would go on to bring us the glories of Vatican II,
2) opened the door (and the floodgates) to evolution and atheistic science in general
3) opened the floodgates to "Catholic birth control" by condoning NFP (even for "eugenic" reasons)
4) started tampering with the Sacred Litrugy (set Bugnini in motion, approved the Holy Week changes, promoted Dialog Masses, and allowed liturgical experimentation like the "Mass of the Future")
5) failed to condemn Cardinal Cushing (and defend Father Feeney), thereby presiding over the complete collapse of faith in EENS and in Catholic ecclesiology ... leading directly to Vatican II
6) sponsored some of the first Ecuмenical gatherings
7) many people try to pretend this is just a modern problem, but the Lavender Maffia was becoming well entrenched already during the reign of Pius XII. Many credible accusations of priestly pedophilia go back to the 1950s.
8) when he found out about Montini ratting out clerics behind the Iron Curtain (leading to their executions), he punished Montini severely by ... sending him to Milan, only without a Cardinal cap.
We can probably think of more ... much more.
Apart from defining the Dogma of the Assumption, which had little practical impact on the Church, what did this man do but destroy and set the stage for destruction?
Was he spending way too much of his time (scandalously) with the Popessa? (that entire thing was a terrible scandal, whether or not anything sinful happened there. St. Pius X wouldn't ride in a carriage with his own sister lest he cause scandal among those who didn't know they were related).