You are applying a modern way of preaching to a first century document.
It might flow just fine as a modern sermon. That is not evidence it was used, intact, as a first century sermon.
I have already acknowledged elements of Hebrews were likely part of separate Apostolic teachings.
The letter is identified by the author as being a letter.
Beyond that, no need to speculate.
Hebrews is a powerful testimony of the superiority of Jesus Christ and the new covenant to the OT Law and the Mosaic covenant that was but a shadow of things to come. I’m certain we agree on that.
No, I am not. Compare Hebrews to Peter and Paul's recorded sermons. See the structure and the intended audience and decide for yourself. I think the argument has merit. It's not something one would ever break fellowship over, but I see the merit in Hebrews being a recorded sermon.