How have we come at the Priesthood in the last days? It came down, down, in regular succession. Peter, James, and John had it given to them and they gave it to others. Christ is the Great High Priest; Adam next. (HC 3:387-388; this infers: Peter/James/John --> Christ --> Adam)
We have discussed this quote a lot already. I don't like your interpretation of this, and I don't think Grindeal would either. I think the Peter, James, and John is instead a reference by Joseph to the restoration of the priesthood to Joseph and Oliver.
Our Savior speaks of children and says, Their angels always stand before my father. The Father called all spirits before him at the creation of man, and organized them. He (Adam) is the head, and was told to multiply. The keys were first given to him, and by him to others .... The keys have to brought from heaven whenever the Gospel is sent. When they are revealed from heaven, it is by Adams authority. (HC 3:386,387; not only does this infer The Father (of spirits) is Adam, but it explicity says he's THE HEAD and whenever keys are revealed from heaven, it's by HIS authority, not Christ's.)
We haven't discussed this quote, however I don't find that it supports your position. "The Father" in this quote appears, to me, to be a separate and more authoritative figure in Adam. I see Joseph implying that the Father is the one telling Adam to multiply and giving him keys.
Here is another clarifying teaching from Joseph, "And again, God purposed in Himself that there should not be an eternal fullness until every dispensation should be fulfilled and gathered together in one, and that all things whatsoever, that should be gathered together in one in those dispensations unto the same fullness and eternal glory, should be in Christ Jesus; therefore He set the ordinances to be the same forever and ever, and set Adam to watch over them, to reveal them from heaven to man, or to send angels to reveal them. "Are they not all ministering spirits, sent forth to minister for them who shall be heirs of salvation?""
I think we can consistently find Adam as the head and set there by Jesus Christ.
What I'm saying with all this, is that Joseph's public discourses probably shouldn't be interpreted as Adam-God doctrine, at least not in a way the places Michael above Jesus Christ. Joseph clarifies many times that he put's Christ above Michael. I'm also saying what Brigham taught was a radical departure from the established priesthood order. If Joseph taught it, and we have been acknowledging that possibility, I do not believed he would have upset his well established priesthood doctrine, and if he did it would also have been a radical departure for him to make as well.