One benefit would be in Perfectae Caritatis. Perfectae Caritatis called upon all of the religious communities to follow the original charism of the foundation of their communities. In the case of the SSPX and other similar communities the fact that the TLM  is an important part of their charism then any attempt to take it away would be contrary not just to the spirit of Vatican II, but also to the explicit instructions of the docuмent itself.  

Try to be a little more fair. First, His Excellency Bp. Fellay doesn't believe what you seem to think H.E. believes, "It is a terrible docuмent, completely heretical, which claims that the Jєωs can be saved without coming through Our Lord (par. 36). Exactly the opposite of what Sacred Scripture teaches us, along with the first Pope himself, Saint Peter, who says this to the Jєωs: “There is no other name under heaven given to men, whereby we must be saved” (Acts 4:12). In other words, there is no other means of being saved except through Our Lord. And here Cardinal Koch thinks that you can make a statement saying the contrary. But, he tells us in black and white (in the Preface): “This is not doctrinal teaching.” http://sspx.org/en/can-pastoral-council-be-debatable

Second, because Vatican II is non-infallible and pastoral - unlike all other previous Ecuмenical Councils - it can be questioned further, "The truth is that this particular council defined no dogma at all, and deliberately chose to remain on a modest level, as a merely pastoral council; and yet many treat it as though it had made itself into a sort of superdogma which takes away the importance of all the rest." (Pope Benedict XVI) http://catholicknight.blogspot.com/2009/02/vatican-ii-was-just-pastoral-according.html

Third, the salvation question has become very confused.  I'm with St. Thomas and St. Augustine. God will certainly bring a pagan who seeks the truth to Christian Faith, and probably bring one who desires Holy Baptism to the Sacrament itself which will save him.

Fourth, as pointed out in the first link, with regard to this thread topic, "In the Council, surely, we find repeated a great number of dogmas; it says that there is the Holy Trinity, that Our Lord Jesus is God, it says all that! They even say, in the Council, that in order to be saved, one must go through Our Lord. That is said in the Council. There was even someone who had fun demonstrating that we were more faithful to the Council than the Jesuits." CCC 848, citing Ad Gentes, and CCC 161, citing Mk 16:16 and Dei Filius from Vatican I, seems to agree with this. But no one is sure - and this is part of the problem - because many like Barron and others openly teach even atheists can be saved as atheists. Such persons, as ABL used to say, should be reduced to perpetual silence.

Fifth, a proverbial 95% in V2 and the CCC can be read in light of Tradition. The main issue in Vatican II was not declared - a dogmatic definition of the Kingship of Christ and the necessity of explicit faith in Him for salvation, the universal Mediation of our Immaculate Mother as Co-Redemptrix with Christ, a dogmatic condemnation of Communism, condemnation of impure publications and the "free love" movement that was beginning, directions to all Catholic states to explicitly honor the Twin Hearts in their constitutions etc.
If those things had been done, the Council would borne good fruit. They remain to be done and must necessarily be done in future.

And the TLM of course should have been preserved unchanged as the only Mass of the Latin/Roman Rite. It must be restored now.