WARNING: The following contains spoilers from Star Wars: Darth Vader #18, on sale now from Marvel Comics.
Darth Vader is easily the most recognizable Sith lord in Star Wars. His trademark Force choke, his blood-red blade and his no-nonsense personality all solidified his everlasting place in villain history. There's no doubt, Vader was impressively strong, but his cybernetic suit severely limited his power. Because of that, he was never realistically able to challenge Darth Sidious for mastery of the Dark Side. However, in a hypothetical world where Vader overthrew Sidious, Darth Vader would probably have been a lousy Sith Master anyway.
In Darth Vader #18 (by Greg Pak, Leonard Kirk, Alex Sinclair and VC’s Joe Caramagna) Darth Vader remembered his disdain for Sidious and reminisced about his fight with Luke Skywalker in cloud City. While reliving those moments, Vader revealed his biggest motivation, and it was pretty simple. He wanted to put a stop to the chaos Sidious instigated and return the galaxy to a place of order. While that may sound like a good idea on the surface, it wouldn’t help his stance as a Sith.
The Sith were always the clear-cut villains in Star Wars. Very seldom did a Sith have even reasonably positive motivation. Of course, Darth Vader became a Sith while trying to save Padme, but after he took on the mantle as a Dark Lord, he embraced all of the Dark Side’s philosophies. As such, he took pleasure in causing fear and was ruthless, brutal and domineering on his quest for power. All of those things were Sith traits, but Vader missed one key aspect of being a Sith.
In Darth Vader #18, Vader revealed his disdain for the chaos that his master always stirred, and that’s a big deal because causing chaos should be a very useful tool for any Sith master. By creating a galactic war, Palpatine used chaos to rise to destroy the Jedi and rise to the role of Emperor. Once he achieved that, he didn’t domineer a lot of his subordinates. He often let them fight for influence because the resultant infighting and back-stabbing led to a chaos that ensured no one of them could become too powerful.
Sidious used chaos, but it wasn’t an original idea; it was a simple Sith principle. Causing chaos and dissent amongst rivals weakens them, allowing the Sith to become more powerful. That’s why, in the Darth Plagueis novel, Sidious' master told him, “‘Through us the powers of chaos are harnessed and exploited … [We will] manipulate events to bring about a storm that will deliver power into [our] hands.” Sure, the Sith were powerful, but why dominate your enemies when they might do it to themselves. Thus, the Sith’s philosophy embraced letting others weaken themselves.
With al that said, if Darth Vader was opposed to using chaos to accomplish a purpose, he would miss the point of being a Sith. Gaining power and domination was the Sith’s highest priority, and being manipulative and conniving was the easiest way to do that. Thus, if Vader only relied on his own strength, rather than using chaos to his advantage, he would be a lousy Sith Master.