That has been my understanding as well, Robb. The presence of the SSPX were not at all helpful. It seems to me that the ordinary lay man and woman and the activities of the Priestly Fraternity of St. Peter did far more to move the reform of the reform along.
Keep in mind that the Priestly Fraternity of St. Peter
was formed from the SSPX in 1988 in the wake of Archbishop Lefebvre's consecrations of the four bishops. Also keep in mind that
Ecclesia Dei, which encouraged bishops to
give permission for the traditional Mass in 1988, was itself a response to those illicit consecrations.
In the early 1980s John Paul II formed a committee to examine whether the traditional Mass had been abrogated, and the committee (of which Cardinal Ratzinger was a member) determined that it had not. But John Paul did not "liberate" (if that's that's the right word for encouraging, not requiring, bishops to give permission for something that
didn't even need permission) the traditional Mass until Lefebvre took the nuclear option (the bishop consecrations) in 1988.
So, yes, the SSPX was critical in the process of liberating the traditional Mass. Want more evidence? Summorum Pontificum was a response to an explicit request by the SSPX; such a liberation was one of the requisites before dialogue could begin again (the lifting of the excommunications was another).
You want another sign? 1962 is an arbitrary date at which to set the currently approved traditional Mass. The traditional Mass underwent reforms in 1964, 1965 and 1967. But the Holy See went back to 1962. Why? Because the SSPX was exclusively using the 1962 Missal in the 1980s when loosening the restrictions was first considered on a major basis.
I am not going to carry the SSPX's water, and I am not a supporter. But honesty demands the admission that they were pretty much the only major force in the Catholic Church in the 1970s and 1980s which refused to accept the unjust and illegal suppression of the traditional Roman rite.