The nontrinitarian case is largely negative and largely the same across the groups: the word Trinity does not appear in the Bible, the technical vocabulary of the creeds is Greek philosophy rather than Hebrew revelation, and the doctrine took three centuries and imperial councils to formulate, which suggests development rather than deposit.
Trinitarian theology accepts the historical premise and denies the conclusion. The vocabulary is admittedly later than the texts; the claim is that it was needed to hold together what the texts assert without contradiction: that there is one God, that the Father is God, that Jesus is worshipped and addressed as God and yet prays to the Father as another, and that the Spirit is spoken of in personal terms. The councils, on this account, were not adding to the material but ruling out readings that would sacrifice one part of it. Nicaea in 325 excluded a creaturely Son; Constantinople in 381 extended the same status to the Spirit; and the earlier condemnation of modalism excluded collapsing the three into one actor wearing masks.
For a comparative reader the useful observation is that strict monotheisms find the doctrine hardest. Islam rejects it explicitly, and the Quran's condemnation of saying three appears alongside a denial that God has a son; Islamic polemic has consistently treated the Trinity as a compromise of the oneness of God, and the charge of shirk, association, is the frame in which it is read. Judaism likewise regards it as incompatible with the declaration that the Lord is one, though medieval Jewish thinkers differed on whether Christianity thereby counted as idolatry for gentiles.
Trinitarian Christians reply that the doctrine is precisely an attempt to remain monotheist, and that any account making Father, Son and Spirit into three gods has failed by their own standard as surely as by Islam's or Judaism's. That reply is not accepted by any of the traditions listed above, and the disagreement is genuine rather than verbal.