Forgive me my brother -
If I were speaking for myself alone, I would of course be wrong...
If for my parish and my priest, I would be wrong...
If for my Bishop or Metropolitan, I would be wrong...
If for but one, My own Pope or Patriarch, I would be wrong...
And if for all the Popes and Patriarchs for a brief time in the history of Christianity...
Even then I would be wrong...
But the Church, you see, is the Communion of all the Apostolic Churches throughout the History of the Body of Christ upon this earth, and the whole of ALL these Sacred and Holy Churches is of ONE accord in this matter of the mortality of the Mother of our Lord throughout the entire history of the world since the Incarnation of God on earth...
For them ALL, Her mortality is DOGMA...
I must agree with you, that there is but ONE Apostolic Communion that has separated Herself from ALL the other Apostolic Communions and CHANGED that dogma into an OPTIONAL belief, and thereby declared Herself to be standing in Schism from the Body of Christ on earth... And within that Communion, the Latin Communion, I agree with you that there are "some schismatic groups (that) believe one thing or the other", but the Body of Christ on earth, the Apostolic Faith of Christ, all and with one accord, receive the Apostolic teaching from tthe very beginnings, that Mariam is Mortal, that She died and was buried... Her bodily Ascension into heaven is not yet a dogmatic tenet, but is received by all as well...
There is only one schizmatic Communion in the entire 2000 year history of the Church on earth that wrongly thinks that belief in Her mortality and death is not a Dogmatic Truth of the Faith of Christ, and believes, as you say, "one thing or the other"... ALL the rest believe ONE thing, and NOT the other...
We can discuss WHY this Truth is true, and WHY one Apostolic Communion alone by Herself has historically come to believe that it is NOT true, but the HISTORY of its reception BY the Church of Christ on earth cannot be contradicted... The Latins are the ONLY Church to officially make this Dogma of the Faith an OPTIONAL belief for Her Faithful... They renamed the Feast Day of the Dormition of the Theotokos to be called "The Feast of the Assumption" falling the same day...
The Church has Spoken in Truth and in Deed on this matter...
Arsenios