Maybe it’s just my interpretation but I don’t see her as THAT powerful. Luke had some training sure, but he was largely self taught and look at how powerful he was in ROTJ, largely on his own merit. Yes he had more time to get there than Rey had, but he’s also far more powerful than Rey has become so the time is spent. Perhaps if you want to analyze it so hard as to calculate how proportionally they each learned per week or something it could seem off, but come on its a movie. They both had the power to become great. One already achieved it, one is still on the journey. Who cares if at point x Rey is a certain level while like was at a different level at the same point, it’s a movie. It’s not like Rey IS as powerful as Luke or any Jedi, she’s just shown to have the potential to be, and probably will be after some time. I don’t see how that’s so far off from Luke who still picked it marginally faster than any jedi was shown to in the prequels. Perhaps teachers and resources for learning just got better over time.