Either I am misunderstanding you or you misunderstood me because I wasn’t clear. I didn’t mean c”v that the Rambam was wrong. Even though he was chozer at the end of his life after he learned nistar, my Rosh Kollel explained to me that it just makes it a machlokes between the first shitah of the Rambam with his later shita, rather than render it invalid.
What I meant was that as The Rambam, it is within his power to maintain such a shita and it be valid. For us though, he is a mi’ut (possibly even against himself) and we have to follow the consensus, not the individual opinion.
What I meant about the Rambam not having Rishonim to hash it out was that, had the Rambam been born now he would be like us, subject to the consensus.