Verse 17"that the man of God may be COMPLETE"
I would think complete means suffecient.
And you would be correct, but there is an important truth you are missing, possibly because you are reading with your anti-catholic glasses?
2 Tim 3:15-4:1
16 All scripture is inspired by God and is useful for teaching, for reproof, for correction, and for training in righteousness, 17 so that everyone who belongs to God may be proficient, equipped for every good work.
Scripture is useful in the hands of those to whom the duties of teaching, reproof, correction and training have been given. And who has the responsibility to carry out these tasks, using scripture?
Eph 4:7-13
7 But each of us was given grace according to the measure of Christ’s gift. 8 Therefore it is said,
“When he ascended on high he made captivity itself a captive;
he gave gifts to his people.”
11 The gifts he gave were that some would be apostles, some prophets, some evangelists, some pastors and teachers, 12 to equip the saints for the work of ministry, for building up the body of Christ, 13 until all of us come to the unity of the faith and of the knowledge of the Son of God, to maturity, to the measure of the full stature of Christ
Jesus gifted the Church with PERSONS whose duty it is to equip the saints for the work of the ministry.
One does not become “complete” by individually reading and interpreting Scripture. Scripture is useful when used by the Church to equip the saints. Those who attempt to equip themselves apart from those gifted by Christ often end up missing the mark.
Jude 1:3 Dearly beloved, taking all care to write unto you concerning your common salvation, I was under a necessity to write unto you: to beseech you to contend earnestly for the faith once delivered to the saints.
Our complete faith has BEEN delivered there is nothing new to add to salvation.
Catholics call this the Divine Deposit of Faith. It was entrusted TO THE CHURCH, and was whole and complete before a word of the NT was ever written. It exists in both forms, the Word of God alive in the Church (Sacred Tradition) and the Word of God in writing (Sacred Scripture).
The Reformers rejected the Word of God in the Church about 500 years ago, and the faith has been more and more deformed ever since.