I guess it depends on how are using “God.” Are you using it to refer to the Divine Nature or the Trinity itself?
Each person is fully God because each Person has the fullness of the Divine Nature. But the Father is NOT also the Son and the Holy Spirit, as distinct persons, so it would be wrong to say that the Father is God as Trinity.
Although, I hope others respond as well, because I still see how this sounds odd. Because we often use God as a catch-all for the Christian doctrine on the Trinity. So often when we say “I believe in one God,” we are saying, “I believe in the Trinity.” But each person is not the fullness of the Trinity. So that would seem to say each person is not the fullness of God, which seems wrong. I hope I’m not committing heresy hahaha.
