I think this is one of those things that people debate and no one knows the definitive answer. I think the Son has always existed with the Father but I can't prove it.That’s right. Which of the trinitarians I quoted ”aren’t trinitarians anymore”?
If we’re going to insist that Tertullian is a trinitarian then we must also insist that trinitarianism teaches that there was a time when the Son did not exist.
I’m not prepared to do that. Are you?