“An infallible magisterium is not necessary to recognize and establish writings as Scripture”
Indeed. All it requires is Your Own Personal Opinion.
You can have it your way.
Calling NARSES!!
Pickup the white courtesy phone.
So rather than arguing that an infallible magisterium is not necessary to recognize and establish writings as Scripture, which you cannot, you presume that the alternative is "sola individualistica" (if there is such a word)?"
This is misleading as as SS disallows claiming assured infallibility, so that neither the individual nor the council are the supreme authority. It was by manifestation of the truth that a general consensus saw writings established as Scripture before there ever was a church in Rome, and which writings the church relied upon. And it is by "manifestation of the truth" (2Cor. 4:2) that the claim to be the church of the living (not dead) God continues to be established.
And yet all individuals, including Catholics, choose what they will believe from pastors, and engage in some interpretation. For they individually first choose to submit to Rome, and then to continue, and then often must engage in some interpretation of what is taught, and what magisterial level a teaching falls under, and thus what degree of assent is required. In addition, your last pope taught that “over the pope as the expression of the binding claim of ecclesiastical authority there still stands one’s own conscience, which must be obeyed before all else..,” even it is not an autonomous and exclusive authority for deciding the truth of a doctrine.
However, under Rome is where "sola individualistica" is supremely manifest, if the pope is not subject to ecumenical council as most Roman Catholics (Bellarmine, etc.) hold, and Dictatus Papae and other teaching affirms (thus no council, not even an Ecumenical one — which he must call and approve — has authority to depose a Pope against his will). Others hold that he is subject to councils, for his “relation is one of neither superiority nor inferiority, but of "intrinsic cohesion."