I agree, Phizzy. I don't think the OT writers had a clue that the Messiah was going to be God (or YHWH) Himself.
See, this is what leads to and cause confusion.
The messiah was not "God Himself", it was the Son of God.
Is the distinction important? Yes.
Why?
To fully understand that when the OT writers and prophets spoke of God, they spoke of The Father and not a "triune deity" that had not been revealed to them yet.
There are clues of course, such as the 3 visitors to Abe and Isaiah stating that the messiah will be called Might God and Everlating Father.
But it is clear that no fist century Jew expected an incarnate Son of God to be the Messiah much less HOW He was going to be the Messiah.