There are a lot of terms not found in the Bible either, so that is a non-starting arguement. Check your dates again. Tertullian's writings date to the end of the second century, less than 200 years after Christ, not 300. Tertullian's formulated of the basic terminology used in formal expressions of the doctrine shows that the doctrine was very mature by the end of the second century.
Going back further Ignatius' (30-107 A.D.) writings contain conclusions that only make sense within the construct of Trinitarian doctrine. Same goes for Justin Martyr (165 A.D.). Theophilus of Antioch (175 A.D.) - first to use Greek trias for "threesomeness" of God.
While it is true that Arius’teaching of Christ being the first creation of God was rejected in the first council of Nicea it was a popular belief.
popular? Short lived with no evidence that the teaching reached back to the apostles as shown by the other ANF above.
There are many hints of the belief of the doctrine we now call Trinity in the early church writers, especially John but they are vague and ill defined.
Such as? John 1 is not vague, Matthew 28 contains the Trinitarian formula recited at baptism for example. The Scripture is also very clear that there is One God - period - yet within that context, the Father, Son and Holy Spirit are God.
. . . . I think there is more evidence that the 1st century beliefs as shown in the Gospels is more likely correct.
Which you have failed to produce. Arianism did not exist with Jesus or apostolic teaching - Trinitarianism permeates that teaching.
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You are a little off in your dates. Tertullian was born approximately 160AD and his writings don’t show up until early in the third century. I’m sorry I said 300 years when I meant third century.