If things were left out that we needed to know, then it would not be possible for Paul to say that it was profitable and could make the man of God COMPLETE.
2 Timothy 3:14-17 But as for you, continue in what you have learned and have firmly believed, knowing from whom you learned it and how from childhood you have been acquainted with the sacred writings, which are able to make you wise for salvation through faith in Christ Jesus. All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work.
Or did God lie when He inspired Paul to write that Scripture was able to make the man of God COMPLETE?
No where in your quote fro 2 Timothy does is say “only scripture.” That interpretation is a manmade tradition of the Protestants.
Scripture is "inadequate", only when it is separated from the Church which guards its true meaning. It is subordinate to the Church which produced it. Hence, the early Church grew and prospered before the New Testament appeared. Paul did not need a New Testament to evangelize the Galatians. The Church did not "come along later and fill it in". First came the Church, then came Scripture.
If things were left out that we needed to know, then it would not be possible for Paul to say that it was profitable and could make the man of God COMPLETE.
It makes the man of God "complete", only when its authentic meaning is understood. When it is separated from the Church which produced it, things are "left out", since the authentic meaning is lost. False understandings of Scripture do not make a man "complete". Quite the contrary. Can you say "Prosperity Gospel"?
Furthermore, there is a critical difference between saying...the Encyclopedia Brittanica is profitable for learning and instruction and making your learning complete" and saying only the Encyclopedia Brittanica is profitable for learning and instruction and making your learning complete". For example, in Paul's letter to Timothy, before he talks of Scripture, Timothy is initially exhorted to hold to the oral teachings—the traditions—that he received from the apostle Paul. This echoes Paul’s reminder of the value of oral tradition in 1:13–14, "Follow the pattern of the sound words which you have heard from me, in the faith and love which are in Christ Jesus; guard the truth that has been entrusted to you by the Holy Spirit who dwells within us" and ". . . what you have heard from me before many witnesses entrust to faithful men who will be able to teach others also".
Here Paul refers exclusively to oral teaching and reminds Timothy to follow that as the "pattern" for his own teaching (1:13). Only after this is Scripture mentioned as "profitable" for Timothy’s ministry.