regarding the hagar and keturah
you are ignoring the plain meaning of a rabbi that says regarding keturah "zoh hagar - this is hagar". But ok, I understand you -have- to ignore the plain meaning if it contradicts what another rabbi says.. Since you assume that all those rabbis opinions are true, and it's as if they came from the same sane consistent rabbi.
and since you don't have ruach hakodesh, you rightly said, your explanation is a -possible- explanation.
Though, as rabbi gottlieb said, "there's always an if". One doesn't really know 100% who one's parents are. Maybe they went to the hospital, found a baby that looked a bit like them, they weren't the parents but they convinced you that they were. It is remotely possible that the world was created 1 second ago. Is it possible that G-d doesn't exist ? Rabbi Gottlieb said, yes! There's always an If.
so the question you would have to ask regarding the explanations you come up with , is how likely is it that they are correct?
There are hundreds of creative explanations that rabbis without ruach hakodesh could come up with. All different. Not all correct.
So since you ignore the pshat of the words of rashi and ramban or of 2 midrashim , on hagar and keturah. You ignore it In favour of these poetic explanations that reconcile the 2. Then you really don't know if you are correct, or the other hundred creative rabbis(without ruach hakodesh) , with different explanations, are correct. And since all the explanations coiuld differ, it may be that only 1/100 of them are correct. Or 1/1000 of them. Or none of them, since there are another million creative explanations nobody had thought of yet, and one of those was correct.
An explanation that is invented, may be implausible.
What If blue elephants exist above your head.. You can't prove they don't. Maybe they do, there's always an If. Or, they may be plausible, simple explanations. But there may be millions of different ones that one could invent..
With this method, the likelyhood of anybody understanding -anything- of any rabbi of that era, is very slim.
Secondly.
Suppose rabbi A says X, and 50 years later, Rabbi B says Not X.
Both rabbis A and B lived in that ruach hakodesh era of rabbis.
Rabbi A 's students wre taught, and believed X. Do they then change their understanding 50 years later, when they hear Rabbi B?
It seems that you are claiming that at the end of that era, we know more about what the original rabbis of that era thought, than their original students. Because we are in possession of more facts, facts that they did not have.
And if you were correct about this idea that the reconciling explanation that reconciles - not just 2, but , say, 10 or 20 different rabbis is correct. Then surely, one would not have to think now for creative explanations to the most obvious problems. Rabbis would have been done already.. especially within that long period you mention, of ruach hakodesh..
one midrash says hagar and keturah were the same, another says not. There are rabbis writing on either side. So why are you the first person to come up with and write down, an explanation to reconcile it?
Why didn't these rabbis, with their ruach hakodesh, write an all encompassing explanation of how both are true..
If it was really the case then it would be absolutely fundamental