This is a category confusion. Christianity is a matter of faith, not objectivity. The truths of Christianity are not necessarily the same as saying "2+2=4".
Firstly the claim about "Christian Doctrine," is not a claim that an examination of how people interpreted Christianity is objectively true!
We find no cases in any human knowledge where such alignment exists except perhaps in mathematics and a few trivia facts in the hard sciences.
My point was that there is a person that existed Jesus of Nazareth and that he claimed to be, and was understood by his followers and his enemies alike to be the messiah is "OBJECTIVELY TRUE OR FALSE."
That his followers were agreed on a center set of facts that could be evaluated to be true or false by their hearers. That Paul argued facts from the OT, and facts of history known to be true by his Jewish hearers. That some of them were compelled to respond based on these arguments.
Those are ontic not epistemic claims! They don't depend on someone's view of knowledge for their truth-value.
Just like 2 + 2 =4 is an ontic claim.
Jesus doesn't become God or creator of heaven and earth due to our belief!
Our self-understanding (epistemic claims) does nothing to change what exists (ontic claims).
Christian Faith is not in "whatever our self-understanding is!" Christian Faith has a locus in history, and its core teaching are known objectively.
Christian faith was in the person of Jesus, and his claims.
Use of "Faith" you describe above is anachronistic. Pistis was similar to fidelis meaning "trustworthy."
When we say Semper Fidelis we mean always trustworth not "these guys are always choosing to ignore the data and just acting on whatever they choose to believe is true despite what is objectively the case or recon tells them or the mission goals, etc."
So "faith" in scripture is trusting in claims that were objectively true. In fact the occasional nature of Paul's epistles were, in the main, Paul decrying other teachers false self-understandings about Jesus, the gospel, sanctification, etc.
The objective basis for Christian belief ought to be the historical person of Jesus of Nazareth. That in my mind, leaves room for a very generous orthodoxy.
So Jesus, and his claims as taught by his followers since Jesus didn't actually write anything. So yes but if my self-understand is that Jesus was just a good man...well that is objectively false.
If jesus was adopted by God and elevated to "a god," again my self-understanding is false objectively.
If my understanding was that Jesus was a God and his Father was another God, then that understanding is again objectively false.
If my self-understanding is that I can get to heaven by way of being righteous through keeping the OT law, then that understanding is again objectively false.
Now like school, we learn a few truths in kindergarten and then more accrue in grade school and so on. It seems that when people just come to the Lord, they should be engaging a few truths. But for someone who has been a Christian for decades and they can't articulate the gospel, or the nature of the atonement, or man's innate nature, well then we have a different problem altogether.
Center set to begin with, followed by an ever-broadening understanding of Christ's work and our work with him.
But I allow children to reason as children. That is I don't stumble newcomers to Christ with the various doctrines of dyophysite christology or distinctions of say homoousios and homoiousios in describing Jesus' nature.