I'm more than happy to accept Rey as some kind of avatar of the Force, where she's guided hugely by the Force to explain her capabilities, but there's got to be some kind of explanation or reasoning as to how that's possible ie what makes her different from everyone else, why the Force needs to work through her in this manner. It doesn't have to be realistic, just consistent with the rules of the fictional universe. It's laid out in TFA as something to be explained in the followup, but in TLJ it's just thrown away and not addressed.
The only heroic figure I can think of that isn't explained, has no meaningful background and just "is", is probably The Tick. That's part of the joke though, that the question is never answered.