The authorities cited do not establish the point. Here's why.
Everyone who denies the presence of a common doctrine practically equivalent to what we now call limbo in the early patristic tradition should read the Catholic Encyclopedia article on this subject found
here which Rhea earlier cited.
Selected Excerpts
There is no evidence to prove that any Greek or Latin Father before St. Augustine ever taught that original sin of itself involved any severer penalty after death than exclusion from the beatific vision, and this, by the Greek Fathers at least, was always regarded as being strictly supernatural.
Thus, according to Gregory[of nαzιanzus], for children dying without baptism, and excluded for want of the "seal" from the "honor" or gratuitous favor of seeing God face to face, an intermediate or neutral state is admissible, which, unlike that of the personally wicked, is free from positive punishment.
In his earlier writings St. Augustine himself agrees with the common tradition ... But this [later] Augustinian teaching was an innovation in its day, and the history of subsequent Catholic speculation on this subject is taken up chiefly with the reaction which has ended in a return to the pre-Augustinian tradition.
Pope Innocent's teaching is to the effect that those dying with only original sin on their souls will suffer "no other pain, whether from material fire or from the worm of conscience, except the pain of being deprived forever of the vision of God" (Corp. Juris, Decret. l. III, tit. xlii, c. iii — Majores).
(Comment: This suffices to establish that no one can accuse this view of being heretical without falling into schism himself, unless he was a sedevacantist who goes centuries back. It is at the least a permissible theological opinion.)
Only professed Augustinians like Noris and Berti, or out-and-out Jansenists like the Bishop of Pistoia, whose famous diocesan synod furnished eighty-five propositions for condemnation by Pius VI (1794), supported the harsh teaching of Petavius. The twenty-sixth of these propositions ... condemned by the pope as being "false and rash and as slander of the Catholic schools" (Denz. 526).
This condemnation was practically the death-knell of extreme Augustinianism, while the mitigate Augustinianism of Bellarmine and Bossuet had already been rejected by the bulk of Catholic theologians.
As to some points raised by you, Gregory,
1. Original sin formally is, in the classic definition of the Angelic Doctor, "the privation of original justice" or, of indwelling sanctifying grace. In no wise, therefore, do I deny that those dying in original sin suffer the deprivation of the beatific vision. This follows necessarily.
And when the indescribable blessedness of the beatific vision that the Saints enjoy in paradise is appropriately understood, it will be recognized, as said in the article, that this is a true penalty indeed, objectively considered, and those who delay baptism therefore sin grievously and incomprehensibly.
2. I believe the above post answers "1 to 4" of your post. Now, importantly, coming to Lyons II and Florence, it must be understood that these are effectively reunion Councils. They did not define new dogmas strictly so called that had not been ironed out in the schools, but proposed to the Greeks and other schismatics the necessary objects of Catholic faith they were bound to confess. In many places these Councils repeat the view of the Angelic Doctor verbatim.
I quote again,
Finally, in regard to the teaching of the Council of Florence, it is incredible that the Fathers there assembled had any intention of defining a question so remote from the issue on which reunion with the Greeks depended, and one which was recognized at the time as being open to free discussion and continued to be so regarded by theologians for several centuries afterwards.
What the council evidently intended to deny in the passage alleged was the postponement of final awards until the day of judgement. Those dying in original sin are said to descend into Hell, but this does not necessarily mean anything more than that they are excluded eternally from the vision of God.
3. You've already conceded that like St.John the Baptist, some were sanctified in the womb. This is the plain teaching of the Angelic Doctor, that some may be subject to a similar cleansing even now, as a kind of privilege and that such actually removes from original sin and is therefore an extraordinary means of the sacrament. This intention then may be raised up to God in prayer and the good God may see fit to grant it through His own means, or the good God may not.
Expecting you to cite the later Councils, I mentioned Suarez who lived after Florence and even Trent as typical of what was recognized by theologians and the Church as open to free discussion. Moreover, Ludwig Ott can accurately be said to represent a peer-reviewed publication the theological consensus of Catholic scholars in the last century, all of whom were well aware of Florence.
So it isn't a question, all told, of the Ecuмenical Councils, but of your interpretation of them which you impose without a mandate from the Church against the studied interpretation of several other theologians in the last century who were never condemned in their day.
4. In the light of all that has been said therefore, even apart from a decision by the Catholic Church which I believe has come, for the faithful Catholic mother, say, who suffers a miscarraige, it would be lawful to submit in prayerful hope to divine Providence the intention of meeting her child in the heavenly kingdom.