Luke isn't OP at all. Rey's feats of power in just Force Awakens rival or surpass what even ROTJ Luke accomplished. Let alone her insane power by the end of Last Jedi.
In A New Hope, the only force powers Luke demonstrates are reflex or intuition based. Things that are traits of all force sensitive people. He already has great skill at piloting and aiming due to this, but this only makes him exceptional compared to non-force sensitive characters. With a few lessons from Obi Wan, he is able to learn basic blaster deflection. An ability the prequel trilogy establishes is one of the earliest and most basic skills preshool aged jedi trainees learned to do. But that's all Luke really does in A New Hope. He also would have failed and died in the Death Star Trench had Han not arrived to ambush Vader.
There's a 2 year time skip between ANH and Empire. The Wampa cave is the first time Luke demonstrates a telekinetic force power. He pulls his lightsaber from a foot or two away, barely managing it with a maximum effort on his part. On Dagobah, Luke makes quicker progress via intense training and instruction from Yoda. His time there is generally thought to be a couple of months. Again, at first Luke struggles to lift small stones. He fails outright to lift the X Wing. At the end of his visit, he can lift several larger objects (R2D2 and some storage crates). He can also jump great heights. But Vader still makes a fool of Luke during their duel on Bespin, beating Luke without even trying.
After another year has passed, Luke has sharpened his empathic and foresight powers. He also now uses mind tricks and can use his father choke ability. Luke does a lot better against Vader, seemingly able to push back (and outright beat him when enraged). Though we don't know if Vader was still holding back or not. Regardless, Luke is still easily overpowered by the Emperor.
We actually witness Luke starting out, struggling to even do simple things, make progress, fail, come back from failure, progress some more, succeed some but still fail some more. And he's given ample time and proper instruction through all of this progression.
The time gap between Force Awakens and Last Jedi is a week or less. Rey starts out completely ignorant about the force, and at the end of Last Jedi she's effortlessly lifting hundreds of massive boulders. In just Force Awakens, she overpowers and reverses Kylo's mental probe (not to mention mind tricking the stormtroopers), beats his telekinetic pull over the lightsaber, and defeats him in a duel. Also having never held a lightsaber before (a metal staff doesn't give you any experience with a weightless blade, especially against a highly skilled opponent with decades worth of experience wielding such a weapon). When she gets to Ach To, Luke doesn't even train her. She stays there 3 days. Luke spends about 30 seconds of the first day trying to show her how to meditate, but he immediately cuts it off and runs away when she uses the dark side to crack the cliff. All Luke does in the remaining time is complain about the jedi order and yell at her when she contacts Ben. Rey finally gives up and leaves the planet in frustration.
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