"Separated brethren" sounds like the people are still going to heaven - "Anathema" has a different sound. The former is the more ecumenical and inclusive post-Vatican-II approach, whereas the latter is the more austere approach the preceded it. Or so it appears.
Is it your position that either Trent didn't mean to condemn folks to hell by using the word "anathema" or that "separated brethren" doesn't mean that we are able to be saved without the removal of that separation?
Well, "sounding like" can sometimes lead one astray. "C0-Mediatrix" sounds like it means Mary is equal to Jesus, whereas the title does not actually have that meaning.
The Council of Trent took place at a time when the Reformation was fresh, and not considered an established fact. The council reformed areas in the Church, agreeing that reform was needed. In other areas, it held the line. The anathemas drew attention to how serious this was, and what was at stake. You were not in communion with the Church, and in danger of hell, if you did not repent. This was a time when going to war to solve a theological issue made perfect sense.
At the time in which Vatican II took place, the Reformation is now an established fact. There are people who left the Catholic Church generations ago, and have no sense of having protested against it. Many of them are in denominations that are off-shoots of off-shoots, for example, the Methodists descend from the Anglicans.
We are no longer living in the time where a king will wait barefoot in the snow for three days in order to have his excommunication lifted. Anathemas, and excommunications of those who are already outside the Church will only push people away, not draw them in. Therefore, the change in vocabulary reflects that.
I do not see that the actual Church doctrine has changed. From the Catechism:
Who belongs to the Catholic Church?
836 "All men are called to this catholic unity of the People of God. . . . And to it, in different ways, belong or are ordered: the Catholic faithful, others who believe in Christ, and finally all mankind, called by God's grace to salvation."320
837 "Fully incorporated into the society of the Church are those who, possessing the Spirit of Christ, accept all the means of salvation given to the Church together with her entire organization, and who - by the bonds constituted by the profession of faith, the sacraments, ecclesiastical government, and communion - are joined in the visible structure of the Church of Christ, who rules her through the Supreme Pontiff and the bishops. Even though incorporated into the Church, one who does not however persevere in charity is not saved. He remains indeed in the bosom of the Church, but 'in body' not 'in heart.'"321
838 "The Church knows that she is joined in many ways to the baptized who are honored by the name of Christian, but do not profess the Catholic faith in its entirety or have not preserved unity or communion under the successor of Peter."322 Those "who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church."323 With the Orthodox Churches, this communion is so profound "that it lacks little to attain the fullness that would permit a common celebration of the Lord's Eucharist."
Dominus Iesus was written after the compilation of the Catechism, and states this more clearly:
IV. UNICITY AND UNITY OF THE CHURCH
16. The Lord Jesus, the only Saviour, did not only establish a simple community of disciples, but constituted the Church as a salvific mystery: he himself is in the Church and the Church is in him (cf. Jn 15:1ff.; Gal 3:28; Eph 4:15-16; Acts 9:5). Therefore, the fullness of Christ's salvific mystery belongs also to the Church, inseparably united to her Lord. Indeed, Jesus Christ continues his presence and his work of salvation in the Church and by means of the Church (cf. Col 1:24-27),47 which is his body (cf. 1 Cor 12:12-13, 27; Col 1:18).48 And thus, just as the head and members of a living body, though not identical, are inseparable, so too Christ and the Church can neither be confused nor separated, and constitute a single “whole Christ”.49 This same inseparability is also expressed in the New Testament by the analogy of the Church as the Bride of Christ (cf. 2 Cor 11:2; Eph 5:25-29; Rev 21:2,9).50Therefore, in connection with the unicity and universality of the salvific mediation of Jesus Christ, the unicity of the Church founded by him must be firmly believed as a truth of Catholic faith. Just as there is one Christ, so there exists a single body of Christ, a single Bride of Christ: “a single Catholic and apostolic Church”.51 Furthermore, the promises of the Lord that he would not abandon his Church (cf. Mt 16:18; 28:20) and that he would guide her by his Spirit (cf. Jn 16:13) mean, according to Catholic faith, that the unicity and the unity of the Church — like everything that belongs to the Church's integrity — will never be lacking.52
So, Christ established only one Church. We cannot all be lumped together as a single Christian entity under the heading of a spiritual Church of Christ.
Then, a little further down:
17. Therefore, there exists a single Church of Christ, which subsists in the Catholic Church, governed by the Successor of Peter and by the Bishops in communion with him.58 The Churches which, while not existing in perfect communion with the Catholic Church, remain united to her by means of the closest bonds, that is, by apostolic succession and a valid Eucharist, are true particular Churches.59 Therefore, the Church of Christ is present and operative also in these Churches, even though they lack full communion with the Catholic Church, since they do not accept the Catholic doctrine of the Primacy, which, according to the will of God, the Bishop of Rome objectively has and exercises over the entire Church.60
On the other hand, the ecclesial communities which have not preserved the valid Episcopate and the genuine and integral substance of the Eucharistic mystery,61 are not Churches in the proper sense; however, those who are baptized in these communities are, by Baptism, incorporated in Christ and thus are in a certain communion, albeit imperfect, with the Church.62 Baptism in fact tends per se toward the full development of life in Christ, through the integral profession of faith, the Eucharist, and full communion in the Church.63
“The Christian faithful are therefore not permitted to imagine that the Church of Christ is nothing more than a collection — divided, yet in some way one — of Churches and ecclesial communities; nor are they free to hold that today the Church of Christ nowhere really exists, and must be considered only as a goal which all Churches and ecclesial communities must strive to reach”.64 In fact, “the elements of this already-given Church exist, joined together in their fullness in the Catholic Church and, without this fullness, in the other communities”.65 “Therefore, these separated Churches and communities as such, though we believe they suffer from defects, have by no means been deprived of significance and importance in the mystery of salvation. For the spirit of Christ has not refrained from using them as means of salvation which derive their efficacy from the very fullness of grace and truth entrusted to the Catholic Church”.66The lack of unity among Christians is certainly a wound for the Church; not in the sense that she is deprived of her unity, but “in that it hinders the complete fulfilment of her universality in history”.67
What I understand this to be saying, and again, I want to caution that I am no theologian, this is just my personal understanding, is that you still need to be a part of the Catholic Church in order to attain salvation. Our separated brethren are still joined to the Catholic Church because the efficacy of their baptism is derived from the Catholic Church, in some way.
The anathemas of Trent were warning a group of people who were leaving the Church that they were in danger of hell by separating themselves from the fullness of Truth. The separated brethren of Vatican II is reminding people who see themselves as having never been a part of the Catholic Church, that they are, in a sense, joined in communion with the Church, and hopes that they will draw ever nearer.
I feel that asking "Can you be saved without joining the Catholic Church" is sort like asking "Can you be saved and never read the Bible?" Sure, you can, but you're missing out on a lot.