Not since the beginning, but 400 years after Christ, written in creeds. The early Fathers certainly didn’t hold such doctrine, it’s not scriptural.
If you want to point out references of them being of one substance, I will yield.
John certainly did believed it. It’s been settled doctrine for eons. It’s definitional. It’s what Christian believe. It’s what seperates us from non-Christian.
I can’t convince you of the truth, only the Holy Spirit has that power.
Post 330 already has the *I and my Father are one* reference. I don't see how it can be stated much plainer or clearer. What are you looking for in the way of statements to prove that Jesus IS God? How could it be stated any better?