One salient point that necessarily has to emerge from these facts is that there is little evidence that many of the ancients ever gave these questions much thought.
Correct. What we see is that the early Christians believed absolutely in the necessity of Baptism for salvation.
If there were not a constant tradition in the Fathers that the Gospel message of ‘Unless a man be born again of water and the Holy Ghost he cannot enter into the kingdom of God’ is to be taken absolutely, it would be easy to say that Our Savior simply did not see fit to mention the obvious exceptions of invincible ignorance and physical impossibility. But the tradition in fact is there; and it is likely enough to be found so constant as to constitute revelation.
It's why the Christians wept so bitterly at the passing away of Valentinian. People SIMPLY believed in the necessity of Baptism for salvation and didn't immediately begin a twenty-minute equivocation about exceptions.
There's no evidence that BoB/BoD considerations were revealed by Our Lord and were taught universally by the Church Fathers.
One can easily imagine the climate in which BoB speculation arose. Perhaps some unbaptized catechumens were martyred, whereas you had some people living sinful lives right up to the end and then receiving Baptism on their deathbeds. St. Augustine explicitly mentions this reasoning, but then in the end rejects it. In other words, this kind of thinking originated in a questioning of what would be fair or right of God to do, but St. Augustine dismissed this pseudo-theological "reasoning" as leading to a vortex of confusion.
At no point was there ANY evidence that BoB or BoD could EVER be applied to anyone other than a catechumen, whom the early Christians formally received with a liturgical ceremony as "Christians" though not "fideles".
This idea that non-Catholics can be saved by some BoD-like mechanism NEVER EVER ENTERED THE WILDEST THOUGHTS OF ANY OF THE CHURCH FATHERS. And THIS is my chief problem.