Emperor arrogance viewed Luke being naive as a weakness when in reality it was his strength.
Yeah sure Luke was about to get hurt real bad but the emperor failed to see past his own arrogance that the punishment he was about to unleash on Luke to teach him a lesson on the power hierarchy was going to create an awakening on Vader which would continue to reverberate for decades later because a reborn emperor failed to learn his lesson that arrogance that comes from power over others gives you a false sense of being indestructible and will eventually lead to your downfall.
A key ingredient in defeating Palpatine if you aren't the Chosen One seems to be asking for help.
Mace arrogantly refused Anakin's assistance and lost.
Yoda arrogantly refused to let Obi-Wan assist him and lost.
Ben Solo tried to stand alone against Palps and lost.
Interestingly enough all three fell great distances as a result too.
But Luke asked for the help of the Chosen One and prevailed. Rey asked for the help of the Chosen One (and a whole mess of other Jedi) and prevailed.
I believe that only Anakin was capable of defeating Palps by himself.
TROS Palps was channeling the power of all the Sith but Rey was able to defeat him by channeling not her own power but rather the power of all the Jedi, which actually made her exponentially stronger than Palps.
Because the self-serving "only two" rule became his greatest weakness in that moment. If you consider two Sith at a time for a thousand generations (25,000 years) that's 50,000 Sith. Whereas Rey was channeling the power of *millions* of Jedi (a mere 200 Jedi per generation times 1,000 generations is 5 million right there.) Palps had no chance and was toast. A nice overlap with "but there are more of us Poe, there are more of us..." taking place above.
It was never Rey's power or the power of her lightsabers if you listen to the dialogue.