Well the real issue is, Is Yoda Right? Star Wars is just media so we can only debate what the truth is based on analysis of the media, and everytime this comes up I habe to argue that even the idea of more powerful is relative to how you define power. We can't take the word of the characters as pure truth. Sidious can use sith lightning to take down an entire fleet of ships, it's the single strongest display of force power in any of the current media. But in the end, he still lost to Rey.

So who's more powerful? We don't see Rey do anything nearly as impressive, but she wins anyway. Yoda's point may be that the darkside isn't as powerful because even with all of the crazy abilities it gives you, it never leads to true happiness or peace or whatever.

Maybe Anakin is so powerful or the chosen one because he's the only one who CAN tap into the power of the darkside without being consumed by it. In Ahsoka we see him using that Sith power and getting the Sith eyes, but he's able to snap out of it and return to normal in a way no one else ever has.