Advent
2.) Can anyone find me a quote that specifically calls Sidious "the most powerful Sith Lord in history" that hasn't already been debunked as open to interpretation?
The one mentioned in Vader: the Ultimate Visual Guide does stand out; there are others that mention things along the lines of how Palpatine "succeeded where all others failed in taming the dark side" (Dark Empire Sourcebook) and how he was "the greatest master of evil ever to use Sith power" (Complete Visual Dictionary). I'd be happy to provide the bulk of them, but that will have to wait until I'm home and able to cite most of my sources.
Advent
"Vader imagined the power that could be his if he crushed Palpatine and established his own rule over the Empire. But first, he would need his own apprentice. By himself, he could not hope to defeat the most powerful Sith Lord the galaxy had ever known."We're given the definition of what 'power' means in the context of this sentence at the beginning. 'Vader imagined the power that could be his if he crushed Palpatine and established his own rule over the Empire'. It's obvious then that galactic dominance and having reign over a militant empire is what 'power' was alluding to. You can't find a single person with
I'm not certain I agree with this line of thought. That Vader mentioned "establish[ing] his own rule over the Empire" does not necessarily refer to either political or militaristic authority; Palpatine's very existence is an impediment to Vader's growth as a Sith Lord, given that the Emperor maintains a stranglehold on all relevant Force knowledge the galaxy abroad; his death would remove an obstacle for Vader's scholarly pursuits without having a higher authority constantly looking over his shoulder and limiting his knowledge base. Especially when one considers that Palpatine used Imperial resources for collecting such information, through dark side adepts and other agents, the term 'power' does have relevance to Force-related issues.
More importantly, where does Palpatine's supreme authority as the head of state or commander-in-chief have anything to do with Vader being unable to "hope to defeat the most powerful Sith Lord the galaxy had ever known?" Rather like Janus's argument against a similar statement from the New Essential Chronology, the conflict being referenced isn't political filibuster or gerrymandering or debates of any kind, but a struggle to the death between two Lords of the Sith. Likewise, would a Star Destroyer be enough to interfere? Palpatine's political and military authority really have no direct reference or consequence to Vader's aspirations: especially when one considers that Yoda himself very nearly got the job done; I don't recall the Imperial Army or Navy being much help to the Emperor then.
Advent
3.) If quotes are the be all, end all...
That's just it: they aren't. To my knowledge, no one has asserted that a quote or statement from any source is automatically correct; particularly if there is direct contradiction from another source. Consider the publisher's summary on the paperback version of Specter of the Past, volume one in the Hand of Thrawn duology: "Hugo Award-winning author Timothy Zahn makes his triumphant return to the Star Wars(r) universe in this first of an epic new two-volume series in which the New Republic must face its most dangerous enemy yet—a dead Imperial warlord."
The statement is clearly out of universe, referencing Timothy Zahn; and yet we, the audience, are to believe that the mere rumor of the late Grand Admiral Thrawn's return is "the most dangerous enemy" the New Republic has ever faced? That would not only surpass the real Admiral Thrawn, but as well as the likes of Zsinj, the Disciples of Ragnos, Hethrir, the Pentastar Alignment, Daala, and the reborn Emperor himself.
The statement is clearly contradicted in the grand scheme of things. Even when one takes into account the accolades of swordsmen such as Anoon Bondara, Kit Fisto, Agen Kolar, et al. one must provide an adequate frame for the statements: is it possible that what numerous sources consider to be three of the Jedi's finest swordsmen were simply utterly inept when faced with a Sith Lord? No; we rationalize it by explaining that Palpatine's command of the Force allowed him to move faster than their own respective command allowed them; it has no bearing on their skills with a lightsaber so much as it does their relative power in the Force.
Advent
There's more than enough evidence that supports the quote in the Official Fact File, which happens to consider it official fact.
I would, again, disagree with you here. Like you expressed to me in a private message, it would be best for you to argue that the absence of proof is not proof of absence, because a comparison of feats between Kun and Palpatine would leave Kun, and anyone supporting him, rather embarrassed.
Advent
Sadow’s gauntlet allows him to focus dark side energy into beams of destructive energy that tear holes through alchemical-enhanced leviathans and temple rock. The beams cause massive explosions that are nearly matching the size of the Sith Wyrm. Upon equipped the gauntlet, Kun's rage is “multiplied by a thousand…then a hundred thousand”. Rage is what the dark sider draws upon to fuel themselves. It should be noted that the Dark Side Sourcebook states that the Sith amulet "radically enhances the wearer's telekinesis".
The presence of the gauntlets radically reduces the impact of the feat itself; Palpatine accomplished all of his [more] impressive feats without the assistance of Force-boosting arcana.
Advent
Kun effortlessly mind controlling the entire Galactic Senate, composed of hundreds of thousands, possibly millions, of sentient beings from all walks of the galaxy. The apparent ease of which he performs the spell (he maintains control even when he makes a mockery of the trial by using the Chancellor as a puppet, and while dueling his former master) suggests that this was far from his upper limit.
Does the spell require constant concentration and maintenance? The term implies a ritual. But, even if I were tempted to play: Kun mind-controlled the Senate; Palpatine mind-controlled the entirety of the Imperial Navy for two decades, used his "mindfogging powers" to assist Imperial engineers in burying a Super Star Destroyer beneath Coruscant (New Essential Guide to Characters), manipulated General Grievous with the Force, and his death severely impacted the mental equilibrium of every Imperial at Endor.
Advent
Against the battle master of the Order and his former instructor, Kun is depicted as toying with the six century old master Vodo Siosk-Baas. The end result is cleaving through Vodo's defenses like he was nothing.
Which, no offense, is nothing compared to Palpatine's defeat of the three Jedi Masters sent to arrest him with Mace Windu, his battles against Windu, Yoda, Galen Marek, as well as his personal murder of Arden Lyn, a twenty-five-thousand year old dark Jedi and the lover of Xendor.
Advent
The stalemate against Ulic Qel-Droma, one of the greatest lightsaber duelists in history, was a battle that "could have gone on for hours" (Dark Side Sourcebook), indicating Kun's stamina and reserves of strength against someone equally as skilled as he was.
Matthew Stover provided a similar quote for Sidious against the [more] impressive Mace Windu, of which you are aware.
Advent
Powerful Sith sorceress Aleema tries to blast Kun with Sith magic, but the assault is shrugged off by Kun without so much as flinching. Then he uses the same ability to knock her out cold.
How powerful is Aleema? I would reference Sidious's performance against the extraordinarily powerful Galen Marek and the subsequent steps Marek had to take (becoming one with the Force, destroying the observation tower) in order to stall Sidious.
Advent
Palpatine has more expansive knowledge by far + a better command over the Force through experience, but Kun is stronger, and combined with his artifacts, Sith arcana, and saber abilities, he's more dangerous.
This would need to be more substantiated. Stronger? How so? More dangerous? How so?