The quote exists, but it wasn't stated to hype up Vader - the contrary, actually. The point of the 80% was to demonstrate Vader's inferiority to Sidious and that he vastly declined in raw power, because his raw potential was 200% the power of Sidious. People using it to hype Vader is the craziest thing ever.
Anakin, as Skywalker, as a human being, was going to be extremely powerful, but he ended up losing his arms and a leg and became partly a robot. So a lot of his ability to use the Force, a lot of his powers, are curbed at this point, because, as a living form, there's not that much of him left. So his ability to be twice as good as the Emperor disappeared, and now he's maybe 20 percent less than the Emperor. So that isnít what the Emperor had in mind. He wanted this really super guy, but that got derailed by Obi-Wan. So he finds that, with Luke, he can get a more primo version if he can turn Luke to the Dark Side. You'll see, as this goes on, Luke is faced with the same issues and practically the same scenes that Anakin is faced with. Anakin says yes and Luke says no.
And when he finds out Luke is his son, his first impulse is to figure out a way of getting him to join him to kill the Emperor. That's what Siths do! He tries it with anybody he thinks might be more powerful, which is what the Emperor was looking for in the first place: somebody who would be more powerful than he was and could help him rule the universe. But Obi-Wan screwed that up by cutting off his arms and legs and burning him up. From then on, he wasn't as strong as the Emperor Ė he was like Darth Maul or Count Dooku. He wasn't what he was supposed to become. But the son could become that.
Registered: Jun 2016
Location: At the forefront of Sheev's armies
You are misinterpreting Lucas' quote. He doesn's say Anakin's potential is 200 % of Sidious'. He merely says that 200 % of Sidious is something Vader can't reach anymore. That's it. Nowhere does he say Anakin's progress would've ended at 200 %. He could very well have gone beyond it - and would have, if the Mortis arc is any indication.
__________________ "Go worth, my child, and impale your enemies with the banner of Sheev." - The_Tempest, Grand Vizier to His Imperial Majesty Sheev Palpatine