The simplistic notion that the Definition of 1950 regarding the Assumption of our Lady somehow constituted the imposition of a 'new' dogma is quite the opposite of the truth. Put crudely, rather than being Doctrinal Augmentationism, that Definition constituted Doctrinal Reductionism.
The first millennium texts common to Rome and Canterbury express a belief common also to the East: that Mary 'underwent temporal death'; that nevertheless she 'could not be held down by the bonds of death' and that the precise reason why God 'translated her from this age' was that 'she might faithfully intercede for our sins'. This is (ARCIC terminology) the 'Ancient Common Tradition', found in the Altar Missal of the Anglo-Saxon Archbishops of Canterbury (the 'Leofric Missal'), the faith of S Odo, S Dunstan, S Aelfheah, S Aethelnoth, S Eadsige and very probably of so many other archbishops of Canterbury stretching beyond Plegmund to S Augustine. She died and was resurrected. Authoritative, surely?
Yet this is not what Pius XII defined. His 1950 definition, as the ARCIC document on Mary accurately reminds us, does not 'use about her the language of death and resurrection, but celebrates the action of God in her.' In other words, Pius XII took a machete and slashed ruthlessly at the Common Ancient Tradition about our Lady's end, not simply by ignoring the apocryphal stories about how the Apostles gathered and what they found in the tomb and how S Thomas arrived late and all the rest of it; but also by pruning away even the bare structural bones of what Christians Eastern and Western had thought they knew: that she died and was resurrected.
The 1950 decree was not the imposition of some new dogma but the elimination of 99% of what the Common Ancient Tradition had for centuries asserted. Those whose instinctive disposition is to avoid speculation about our Lady's End ought to applaud Pius XII and the radical austerity, the innovative agnosticism, of his definition. He went almost all the way to meet them.