A few thoughts:
What is SS meant to mean ?
Does it mean that Scripture is God’s only canon (= measure/ plumbline/) for Christian theology ?
If so, I think it can be defended. Not by Protestants only
“But the Church was earlier than the NT” In time, yes (in some sense) - but in value/dignity/
authentia ?
An analogy from St.Thomas’s discussion of the Hexaemeron (the work of the Six Days of Creation): The ordo intentionalis (= what God meant to do) of creation is logically prior to the actualisation of the ordo creationis (= the doing of what God meant) - yet the ordo creationis is better, because a more complete reality, than its existence in the Mind of God. An apple that man can see, smell, taste, and enjoy, is
more complete than the un-real-ised
idea of that apple in God’s intention: the apple becomes more of an apple by being given away.
Likewise, the NT is - possibly - nobler in divine “authority” than the Church - the Church, that is, on earth. One is the written word of God, and so, is analogous to the Word made flesh; The other is that Word’s Mystical Body. One is Inscripturate, the Other is Incarnate. The Word is the model both for the Holy Book and for the Holy People; each is related to Him, in different and equally important ways. Either one is better than the other, but, in different aspects. One is Word, One is Body: He alone is Word
and Body. He combines in their rightful pattern things we isolate from that pattern, and set at odds with each other.
So maybe arguing the relative excellence of one compared with the other is an incomplete way of trying to account for their value - both are from Christ. Trying to put one over the other, is like the disciples competing with each other to be be “first” in the Kingdom of Heaven: it’s
a wrong question. Christ is First - and First as man too, because He made Himself the least and last.
ISTM that one should look at what authority is, and how it is expressed, and what is for. “Sola Scriptura” - which may be meant as “Scripture alone”, or “by Scripture alone”: far too many people these days do not understand Latin, let alone Latin grammar, let alone books in Latin that use its grammar - is not a “free-standing” doctrine - it is part of a “body of divinity”. It has a setting, a context. And a purpose. Which is to cast light on how the Christian Faith is to be expressed. Does it do that as well as it could ?
Does it need to be completed by other doctrines ?
Does it express something which could be better expressed in some other way ?
It is wrong, and if it is, how is it wrong ?
Does the Church already say what it expresses, and if so, how ?
Is it an element of Catholic tradition that has been overlooked and so, become Protestant by default ?
Is it a thing the Church might profitably learn from non-Catholics ?
Or is it complete and total garbage of no use to man or beast or Christ ? (Can a thing be that ?)
What do Protestants mean by their theological concepts ?
Ask a Protestant theologian; or read one of them - such as Karl Barth, or Luther, or Calvin; or someone else.
Just as Catholics have beliefs in common, with different insights on to what all hold as true, so do Protestants. What looks like chaos, is often not chaos, but the variety which comes from being an organic, and healthy, reality. Shinbones are not the liver: but they would be foolish to compete with one another. The body and its parts are interdependent. they are made for service to each other. That is not stagnation, nor is it chaos - stagnation is a very Catholic temptation, chaos a very Protestant one: both are unhealthy, in different ways. ##