He was there from the beginning

A Trinitarian question.

For a Christian who confesses God as Father, Son, and Holy Spirit, isn’t the idea of pitting Jesus against the portraits of God in the Old Testament a misunderstanding of what we mean by the word “Trinity”?

Don’t we confess that the Son — the eternally begotten one — was fully present, active, and revealed in the Old Testament as well as the New? In Genesis 1, the son was present. At the burning bush, the son also said “I AM.” Through the whole story, the Father, Son, and Holy Spirit were three-in-one.

Or am I getting my Trinitarian theology wrong here?