Same is true about early belief in Jesus’ divinity. These were definitively not late additions, but very early beliefs.
One of the great historical puzzles of 1rst century Palestine is Paul. He wasn’t with Jesus, but a well known and devote Jew who opposed Christians. Yet he comes to take beliefs that (as you have rightly noted) are a large departure from most of Judaism after Jesus. Why is that? How did that happen?
It isn’t like the tautological claim that “Jews of today don’t believe Isaiah 53 refers to Jesus.” Well duh. If that wasn’t the case they wouldn’t be Jewish (or they would be Messianic Jews). That is a purely tautological claim.
The situation with Paul is different. It would be as if the Pope or a Cardinal suddenly converted to Islam. It is nearly inconceivable that this would happen. Of course, we can imagine a Catholic on the fringes of Catholicism converting to Islam. It is nearly inconceivable that the Pope or a devote Cardinal were to convert to Islam. Now imaging that this new convert quickly becomes the most important theologian in Islam. It would be entirely stunning. That means he wasn’t coerced, and all these non-Catholic Muslims come to trust him very quickly, and he even forms core parts of Islamic doctrine taking it into new directions that people didn’t expect.
Of course it could happen. It isn’t impossible. If it did happen, it would be a gigantic puzzle that would have many people trying to figure out. Simplistic explanations would fail. Clearly he didn’t convert because his family was being held hostage; that wouldn’t explain how he became the foremost theologian in Islam, nor did he even have a family any ways. Clearly it wasn’t because he was a useful figurehead for publicity, because he ends up substantially changing their beliefs.
Something bizarre is going on, and it would be come one of the most important mysteries in history if no coherent explanation could be given. Something out of the ordinary.
This is close to what is going on with Paul. It just doesn’t make much sense what happened, unless of course there was something to the early beliefs of the Church, and that Jesus really did appear to him.
I note also that there is nothing like this in the origin of any other religion. Islam doesn’t have anything odd like this in its origin. There is something different going on with the early Church. You can despise what the Church did later in history (and I’m certainly no defender of its errors). Something different was going on in 1st century Palestine.