Well it could easily be mentioned in a sourcebook. I'm not sure if it has been, but I've not heard anything. Vader could also point it out, He does praise his abilities sometimes.But I'm not sure why we should just assume he's completely mastered Juyo unless that's confirmed for us somewhere.
Sourcebooks are based on info provided by actual books, games and other material. The TFU book lacks such info, thus sourcebooks will not have it either.
Also, info in books is subject to author's interpretation and opinion. For example, complete encyclopaedia states that Marek "ultimately was no match for Palpatine's power", however, that's not what happened in the book.
According to the script he battered Sidious in the Saber match. And at least matched him in their Force contest.
Yes, it is possible that he disarmed Sidious. They fought on platform, which gave Yoda advantage. Sidious couldn't move around and was statically staying in one place, while Yoda still could jump all over the place.
As for power Yoda failed to absorb his lightning at beginning. On platforms Sidious was throwing multiple platforms, while Yoda mostly dodged. Imho Yoda used Force more wisely conserving energy, which allowed him to stalemate Sidious at the end.
Vader on the other hand has been canonically confirmed by Lucas to be 80% as powerful as Sidious. Lucas also states in the ESB Audio commentary that Vader has "lost a lot of power in the force," comparing ESB Vader to pre-injury Anakin.
True. However, it's rather vague statement.
Let me throw a few other canon examples.
Lumiya - she was more machine than Vader.
"The Force is the energy of the living. You interact with it, its eddies and flows, with your own living body. It's all right to have a mechanical part or two-an implant, a replacement foot. But for true Mastery in the Force, light side or dark side, you have to be mostly organic. I'm not, and so the greatest, the most significant powers, I can never learn."
Limiya stated that greatest powers cannot be learned, however, she never said that her regular powers got weaker.
"Nelani tried again, this time with the bust of the Bothan. It reached a halfway point between her and Lumiya, but the older woman reached out with her own free hand and the bust stopped in midair. Now it strained forward toward her; a moment later, it crept back through the air toward Nelani. It was a piece in a game of push-of-war between the women, and neither was winning.
The strain showed in Lumiya's voice, causing it to hoarsen.
...
Lumiya cast a sideways glance at the bust hovering between her and Nelani. It was beginning to creep back toward her, and the strain of keeping it at bay was showing on her face.
...
Lumiya closed her eyes and strained, but the bust still moved toward her.
...
Her last words were little more than a gasp, and her control slipped at that point."
Her Force struggle demonstrates that she is not weak in the Force, however, she gets exhausted faster than normal Force users. She was still capable to fight Mara and Luke on even terms. Even angered Luke only drove her back instead of outright stomping.
I think the way Lucas portrayed the Force is that greater power gives greater Force reserves, not stronger Force attacks. And I can support this idea with loads and loads of evidence.
Most notable one is Kenobi stalemating Anakin's Force push.
Yoda was more powerful than Dooku, however, he couldn't simply disarm him like in case with Ventress.
Yoda stalemated Sidious but them having perfect equal Force potential would be way too big coincedence. They had equal Force mastery but Sidious as more powerful had larger Force reserves.
I, also, can give many examples of prime Luke struggling against inferior Force users as well as stalemating far more powerful ones to support this idea.
Characters like Yoda, Windu, Dooku and especially Kenobi demonstrated that it is possible to stalemate far more powerful users both in combat and Force.
Back to Vader. Even in TFU II the clone was nearly getting overwhelmed by Vader's TK but after some struggle was overpowering him. It supports the idea that Vader's TK is as strong as prior to losing body parts as he still has got the same medichlorian count. However, on entering a Force contest he gets exhausted very fast and loses control.
According to Tempest a recent issue of Insider also claimed Yoda may be most skilled Saber duelist in the history of the Jedi.
Is it canon source? In any case whatever skill he had, he still has got a lot of physical limitations to deal with. Vader is, also, one of the most skilled saber combatants, so Yoda is not above him in that regard.
If he was really Zonakin, Windu, Sidious level in Sabers, we really should have seen a few Saber Stomps Imho.
Anakin never stomped anybody in sabers.
Kenobi couldn't even stomp Mandalorian in sabers. Windu never stomped anyone.
Also, if you mention "Zonakin", Zomarek struck Vader with lightsaber several times before Force handling him.
Also, I will refer to interpretation above that even with suprerior power he still needs to outskill other inferior characters that also achieved mastery in Force and combat or at least fight them until they get exhausted.
Actually yes it did look like he was trying to overwhelm Kenobi. The proof is the second Obi-Wan put his guard down he cut him down.
Nope. He and Kenobi were chatting, until Luke showed up, which provoked Vader to cut conversation short. )
He was gonna kill Kenobi but he wasn't in a hurry.
"Last time we met I was nothing but the learner and now I am the Master". - According to Vader's opinion he improved since, not other way around. But you still can dismiss his opinion as a rant of an insane elder. 😄