Yes, Scripture Alone as the Final (Not Sole) Authority is Sufficient
Roman Catholics have had a long animosity with the doctrine of Sola Scriptura. They think it's Bible plus the traditions of the Roman Catholic institution. A poor understanding of the doctrine has led to confusion.
Let's first define what is Sola Scriptura
Taken from In the Habit of Goring - the article called "What's the difference between Sola Scriptura and Solo Scriptura" clears the misconception behind Sola Scriptura:
Sola Scriptura: the Bible is the only “rulebook” that sets out Christian doctrine. Although we don’t need anything else to know God and be saved by him, God didn’t deliver it in a hermetically-sealed chamber; rather, he put it in the middle of a vast library full of other sources that help us understand it better.
Solo Scriptura: the Bible is the only “rulebook” that sets out Christian doctrine, and any attempt to nuance or finesse our understanding of it using other sources of knowledge is probably from the devil. We don’t need that malarky, we don’t want that malarky, and in fact, you should all probably split up and each go into a separate forest with your Authorized Version and read it alone for the rest of your lives like hermits.
From the Gospel Coalition in the article "Sola Scriptura Does Not Mean Scripture Is the Sole Authority" also has the following statements:
Step #47 [in Smith’s 95 steps to move from evangelicalism to Catholicism] is to “realize that the doctrine of sola Scriptura is itself not biblical but, ironically, is received and believed as a sacred (Protestant) church tradition.” A neat bit of jiu jitsu, but the next sentence makes one suspect that he’s played dirty: sola Scriptura is the belief that Christians have “the Bible alone and no other human tradition as authority.” Later, he challenges his readers to find biblical passages that teach that “Scripture or the written word of God is the sole and sufficient authority for Christian faith.”
Now, I imagine that there are people who believe sola Scriptura as Smith describes it, and Protestants have always insisted that Scripture is a sufficient revelation of God’s will for us (cf., e.g., WCF 1.6). But neither the Reformers nor their heirs concluded that Scripture is the “sole” authority, nor did they deny the relative authority of human teachers. (If Calvin believed the Bible was the “sole” authority, why so much effort and time devoted to reading Augustine and Chrysostom?) As Smith himself points out, the Scriptures themselves point to human teachers and leaders who are to be honored as authorities. Smith is also correct that the New Testament writers encourage Christians to honor apostolic traditions. No argument there, but that’s because Smith has missed the point.
The argument is not about “sole” authority but “final” authority.
Obviously, the apostate mentioned in the article (and 1 John 2:19 talks about such people weren't truly saved) had problems understanding Sola Scriptura.
Some Scripture or all Scripture?
Here's what 2 Timothy 3:14-17 says and I'm taking it from the Good News Translation (GNT):
14 But as for you, continue in the truths that you were taught and firmly believe. You know who your teachers were, 15 and you remember that ever since you were a child, you have known the Holy Scriptures, which are able to give you the wisdom that leads to salvation through faith in Christ Jesus. 16 All Scripture is inspired by God and is useful for teaching the truth, rebuking error, correcting faults, and giving instruction for right living, 17 so that the person who serves God may be fully qualified and equipped to do every kind of good deed.
It's really irritating that there are still objections there because they don't understand the Bible. However, I'm not talking about any ordinary scripture but the Holy Scriptures. Scripture is referred to what religions refer to as what they consider as their sacred text. When I'm talking about Scripture here - I'm talking about the holy writings in the Old Testament and the New Testament. Roman Catholics say that 2 Timothy 3:14-17 doesn't say the Bible is sufficient in itself. They also say that the apostles never carried a Bible. However, do they realize that the apostles in writing the New Testament strongly quoted from the Old Testament? Do they realize the words "it is written" is even found in Roman Catholic-approved translations of the Bible?
What can be found when we analyze the verse from the GNT? We can see the power of how the Holy Scriptures led Timothy to salvation. Paul also mentions that the pages of the Scriptures at that time (which wasn't the complete Bible yet) were all-sufficient. If you were living in Joshua's time then the guidance contained in Genesis up to Deuteronomy was all-sufficient. Paul mentions the fact that not some but all Scriptures are inspired by God. All the books of the Old Testament were God-inspired. Who gave Moses the entire Mosaic Law aside from the Ten Commandments? God! Who gave the prophets the words that they had to speak? God! Then you've got some Roman Catholic amateur "apologists" who said that following the Bible alone led to evil. It's time to ask them whose words are in the Bible? Is the Bible the collection of the Scriptures or not? If they say trusting the Bible alone as the final authority leads to evil then are they saying that God's Words are not pure? If that's so then God can no longer be holy and just. If God could be wrong and could sin then He isn't perfectly holy. The perfectly holy God is never wrong meaning He can't be wrong. Sin in itself is error and a mistake. Since God can't be wrong then He can't sin either. So why are they saying Sola Scriptura supposedly led to evil? That's a very confusing heresy right there!
What can be found when we analyze the verse from the GNT? We can see the power of how the Holy Scriptures led Timothy to salvation. Paul also mentions that the pages of the Scriptures at that time (which wasn't the complete Bible yet) were all-sufficient. If you were living in Joshua's time then the guidance contained in Genesis up to Deuteronomy was all-sufficient. Paul mentions the fact that not some but all Scriptures are inspired by God. All the books of the Old Testament were God-inspired. Who gave Moses the entire Mosaic Law aside from the Ten Commandments? God! Who gave the prophets the words that they had to speak? God! Then you've got some Roman Catholic amateur "apologists" who said that following the Bible alone led to evil. It's time to ask them whose words are in the Bible? Is the Bible the collection of the Scriptures or not? If they say trusting the Bible alone as the final authority leads to evil then are they saying that God's Words are not pure? If that's so then God can no longer be holy and just. If God could be wrong and could sin then He isn't perfectly holy. The perfectly holy God is never wrong meaning He can't be wrong. Sin in itself is error and a mistake. Since God can't be wrong then He can't sin either. So why are they saying Sola Scriptura supposedly led to evil? That's a very confusing heresy right there!
They also say that a lot of Old Testament verses to defend Sola Scriptura were well written in the Old Testament. I can agree that the canon is still not complete during the time Deuteronomy was created. Yet, we do realize that when a new book in the Bible is written - it doesn't contradict previous entries. The prophets came and they relied on the writings before them. The apostles came and they knew the authenticity of the Scriptures before them. Jesus pointed to the Old Testament and mentioned in His temptation (Matthew 4:1-11, Luke 3:1-13 the words "it is written" to refute Satan. He has mentioned Scriptures to the point of saying "Have you not read?" or "Did you never read in the Scriptures?"
Why Roman Catholicism rejects Sola Scriptura is because it hates the doctrine of assurance. If people relied on the Bible more than Rome then much chaos can happen. It's necessary to always condition people that the Bible is important but what the priest says is way more important, right? If they have themselves trusting the Magistrate over Scripture then it's easy to control them. Just remember that even the Latin Vulgate (Catholic Bible) wasn't even allowed to be ready by lay Roman Catholics. All Luther had to refer back then was a Roman Catholic Bible before the Reformation swung open. All William Tyndale had was a Roman Catholic translation to translate into vernacular. Sadly, such information is withheld from the poor Roman Catholics today.
What's also more interesting is that from a Roman Catholic site called Homiletic and Pastoral Review also an article called "What Evangelicals Can Learn From Catholics". Here is a pretty interesting excerpt where they inadvertently end up admitting their flaws as a cult:
The ideal Evangelical sermon not only teaches the meaning of the biblical text, it also applies that text to the real-world concerns that the members of the congregation face. Many pastors use expository preaching, which means the pastor will have a series of sermons on a single book of the Bible. Each week, the sermon explains another section of the book, verse by verse, so that by the end of the sermon series, the congregation has a good understanding of the main message of the book. Sadly, expository preaching is probably the biggest reason that Catholics leave the Church in favor of an Evangelical congregation. Ex-Catholics often say that they understood the Bible for the first time after regular attendance at an Evangelical church.
I'm just thankful to God that even if the numbers aren't huge but it can't be neglected. I don't care if there are over five billion Roman Catholics. If at least one in every 5 of them starts leaving for the truth then that's good news. I'm glad for every Roman Catholic who is interested in knowing the Scriptures better. They are in need of evangelism one way or another.