I can make an argument.
CMRI strongly advocates the notion that there can be salvation outside the Church. Yet all the alleged error in Vatican II derives logically from the same position on EENS that the CMRI hold. Consequently, they have no doctrinal justification for refusing to be subject to the Vatican II hierarchy. Consequently, the CMRI are schismatic.
As always the Church INCLUDING CMRI, teaches NO SALVATION OUTSIDE THE CHURCH, and also as always, the Church teaches that no one, not even Ladislaus or Stubborn or Cantarella can judge who exactly is outside the Church, because God give His graces to whomever He desires and whenever He desires. This is what I was taught way before Vatican II.
This grace is rare and not the norm, but it can happen because the Church says so.
Vatican II however is schismatic because the moment the
ConciLIAR "popes" have contradicted God they became a new religion. Example: I am the Lord Thy God and THOU SHALT NOT have strange gods before me. The Bible states to leave the Harlot, (interfaith).