The light side is said to be stronger than the dark, but Palpatine's connection to the Force appears to have grown far stronger in Return of the Jedi. So while Luke may have bested him in terms of athletics, Palpatine's Force-powers could very likely give him the victory.
Luke did INDEED become Extremely powerful, basically on the level of Superman with the Force. It was said in one of the EU books that Anakin and by extension, Luke and Leia, had TWICE the midi-chlorian count as Palpatine.
Snoke's biggest goal during the Star Wars sequels was to find and kill Skywalker before he joined the fight against the First Order, which shows that Sidious was afraid of Luke. Those are canon arguments for why Luke Skywalker could defeat Palpatine.
Admittedly, Rey skills couldn't possibly be as developed as Anakin's or Luke's. Nevertheless, considering how fast of a learner she is, and how unique the powers she possesses are, it's not a stretch to say that Rey could be a more powerful Jedi than Anakin and Luke Skywalker.
If Luke Skywalker turned to the Dark Side, only his father, sister, his or her children — either fully trained, or Abeloth, could stop him. The dark side isn't more or less powerful than the light side. It's just more teachings to learn from. Similarly, any sith who learned from a jedi, would also get more powerful.
Why Palpatine Said Luke was STRONGER in the Dark Side Than Anakin - Star Wars Explained
Who is stronger Luke or Kylo Ren?
This caused him to attempt to assassinate him in his sleep. Needless to say, Kylo Ren is almost definitely a significant threat. However, we cannot definitively say that he is more powerful than Luke. Kylo's powers are vast but they are still highly unbalanced and difficult to control.
Kylo lost to Rey in TFA because he was heavily wounded and was holding back against her due to Snoke's request that he bring her back to him alive. He is also stated by Palpatine in the Secrets of the Sith book to be “equally as powerful as a real Sith despite not being one”.
The realistic answer seems to be, yes, Anakin in his prime could have defeated Luke Skywalker (in the current canon) if they battled one-on-one. The main reason behind this is Luke's lack of formal Jedi training, at least when it comes to combat.
Speaking for Legends, the best Sith Lord to rival Palpatine is Darth Vitiate, also known as Valkorian and “the Sith Emperor”. He consumed all Force energy and all living things on Nathema and Ziost, turning them into Forceless and lifeless voids.
Vader knew that he could never defeat Palpatine by himself (especially after his master bested him on Exegol as well), which is why he tried to recruit Luke to help overthrow him during the Empire Strikes Back. He may have not been able to overthrow the Emperor, but he could throw him over the railing to save his son.
So while Luke may have bested him in terms of athletics, Palpatine's Force-powers could very likely give him the victory. So while fans may never know for sure, it would've likely been a very close battle, with neither side being a clear victor.
Legend had it that Yoda—a Jedi who became Grand Master—was trained by N'Kata Del Gormo. A Force-sensitive Hysalrian, N'Kata Del Gormo was trained in the ways of the Force and achieved the rank of Master within the Jedi Order.
Now in terms of actual power, with both of them at their peaks, Anakin would mop the floor with Rey. Anakin not only has more force potential, but has gone through much more force use training, actual field combat, and is known to be the greatest lightsaber duelist of all time.
Summary. Rey gained knowledge and skills through her connection with Kylo Ren, allowing her to tap into his training and skills. Kylo Ren was wounded by Chewbacca's bowcaster, which he believed inhibited his ability to defeat Rey.
This isn't a fight, this is a curb-stomp. Kylo would absolutely never decline a fight with Darth Vader, a force of legendary power whose surpassing will certianly gain him a place among the most powerful of the Dark Side, but he is clearly outmatched in power.
But to be fair, we really don't ever see Luke face off against anyone strong after Vader so it's hard to say how strong he actually got. Not. They are weaker than Darth Maul. Rey is more powerful than everyone.
Wise, powerful in the Force, and skillful with a lightsaber, Yoda was synonymous with the Jedi Order and trained countless future Jedi. There was no opponent in the galaxy who did not fear Yoda – even Palpatine knew that the little green master could defeat him. As such, prime Yoda could beat Luke.
Summary. Palpatine's true source of power comes from his intense hatred for everyone in the galaxy, which only fuels his strength. Not only that, but the more people hate Palpatine, the stronger he becomes as well, making inspiring hatred a crucial part of increasing his strength.
Thus, while Qui-Gon was less powerful than the likes of Yoda and Mace Windu, Palpatine feared him more. In simplest terms, he was a wild card, and with the Sidious executing an intricate decades-long plan to seize power and destroy the Jedi, a wild card was something he just couldn't afford.
