I agree with you that at a purely philosophical level, ‘God’ is metaphor.
This, however, is the rationale for which we refer to God in context of Christian beliefs as ‘Father of our Lord and Savior Jesus Christ’.
Whenever we refer to God as Father of our Lord and Savior Jesus Christ, or simply as The Father, or Our Father, we no longer refer to a metaphor. We refer to a specific entity who has revealed His essence to us, both in Christian Scriptures and in person of Jesus Christ.
Perhaps you are leading up to this in a sequel post, and I am throwing in a spoiler. But I could not ‘clap’ for your post, and not simultaneously post this response.