I agree that the Rey as a Force creation by Palpatine is the closest we’ve gotten to solving this puzzle. It is tantalizingly close to working for me, and solves a lot of other mysteries as well.

But there still exists that fundamental incongruity with TLJ.

Stepping back a bit, I just had a thought about TROS that seems obvious now but hadn’t considered before: Why do we assume that Palpatine’s children and grandchildren would be strong in the Force?

Granted the Skywalker’s power in the Force seems to be preserved through lineage, but that doesn’t seem to be true for anyone else. Well, perhaps Yoda’s offspring, if that is indeed his offspring, but that just raises the question of why the Jedi wouldn’t raise families if it’s likely their children would inherit their power. I think it’s better than even odds that any spawn of Palpatine would have no power in the Force. In fact, why would Palpatine have offspring if they could potentially become rivals?

I realize that this is somewhat tangential to the current discussion since we’re working off of a different theory now, but it may stand examining if we are to figure out just what sort of Force user Rey can be. By the methods in use by the Jedi Order for over a thousand generations, a powerful Jedi coming from a random family would be the norm, not the exception.

The point here is that the theatrical version of TROS is somewhat incoherent because Rey being a Palpatine shouldn’t be a strong predictor of her abilities, or her affinity for darkness. This means that Rey being a Palpatine must be something other than genetic for it to be strongly meaningful.