With all due respect to the Archbishops, his arguments do not hold water in that they are inconsistent with what followed the 1962 Missal. He was merely appeasing Rome with this determination against Frs Cekada, Sanborn, and Kelly. As Bishop Sanborn stated recently in an on-line interview, he was clearly preparing the way for a Rome reconciliation and the dismissed priests were not.
Quo Primam protects the right of priests to offer the Mass, unreformed from the Mass of Pius V. To wit, there were reforms to the Mass subsequent to 1962 and before 1969 which allowed for more of the Mass to be offered in the vernacular and did not shorten the Mass much more than the second Confiteor and the Prayers at the Foot of the Altar. And since the prayers at the foot of the altar are omitted even in the pre-55 and 62 books on certain occasions, one cannot argue that this omission would be detrimental to the faith.
So using the Archbishop's reasoning and given that he considered Paul VI to be a valid Pope, why not demand that the Mass be said according to the 1964 or 1966 reforms? The English translations are pretty much what you will find in the English translations of the 1962 Missal with the canon in tact.
The Archbishop was simultaneously appeasing a faction of the Vatican as they prepared to release the ultra-restrictive Indult of 1984 to allow the offering of the 1962 Mass, while trying to uphold a close adherence to the Mass of Pius V. But his argument is inconsistent. Fr. Cekada and his priests had every right, via Quo Primam, to offer the unreformed Mass and the Resistance priests have the same right, if not the duty to do the same.