Anakin -- and by extension Vader -- is no slouch when it comes to sword-play. Before he was corrupted, Anakin was regarded as one of the finest duelists the galaxy had to offer. He accelerated at such a pace he came closer and closer to killing Dooku throughout the Clone Wars. Way before he even reached his peak in RoTS.
The attack on the Jedi Temple's an example of this, Cin Drallgis -- a Jedi Battlemaster, and head of the Temple Guard, was held off by Vader using one hand. Later on, he goes on to match Obi Wan in a weakened state. After gaining his cybernetic body, Vader goes on to lead the hunt against the Jedi, train the Inquisitorius, and become stronger and more skilled then ever.
I'm not sure what RWBY's scaling chain is, but I'm willing to put the edge in the Sith Lord's favor.
At the bottom of the skill chain is aura users as a whole. While every living being in RWBY technically has Aura, actually being able to utilize it for things such as defense, regen, and senses requires years of training and a high enough degree of martial skill (and yes you actually need martial skill for it) that only a small percentage of the population of the entire planet ever become skilled enough to utilize their aura. Of that small percentage, an even smaller percentage ever become skilled enough to manifest/control a Semblance (yes semblances are also skill-based). To reach this small percentage comes to the second half of the bottom of the chain: Almost every character worth their salt in RWBY has spent their entire life training in combat and can fight hordes of Grimm with little issue (Almost because Jaune exists). The entirety of the main cast of RWBY was initially enrolled at Beacon Academy, one of the most prestigious combat schools in the world, with almost everyone who was accepted there having been trained for almost their entire life to fight monsters, and each one that was not professionally trained requiring a skill display overseen by Ozpin, who has the composite skill of several thousand professional huntsmen that he accumulated over his immortal lifetime.
TL;DR, Skill Baseline = Having a lifetime of combat training, being able to solo hordes of monsters that can easily kill you if you make a single mistake, being part of the single-digit population of the planet skilled enough in martial combat to be able to subconsciously project your soul as a defensive barrier and being skilled enough in martial combat to project your soul as a superpower, and being recognized as one of the most skilled fighters in the world by a guy with millennia of composite combat skill
Thats the baseline for skill in the verse.
Ruby is well above the average Beacon student, noted as always excelling above her peers in combat training, to the point that even though she was two years away from being eligible to join Beacon she was admitted due her combat prowess impressing Ozpin, with him noting that she was already a master at wielding one of the most dangerous weapons ever designed (Again, Oz is tens of thousands of years old and has spent the majority of his lifetimes training in combat as well as training other huntsmen and even entire armies). Even before the Beacon Arc Ruby had been personally trained by her uncle Qrow, one of the most skilled professional huntsmen on the planet, and had heavily inspired her fighting style from his. In combat Ruby is capable of taking on entire hordes of Grimm on her own and walking away without a scratch and utilizing the different functionalities of the Crescent Rose, such as the massive recoil from the rifle aspect of the weapon and the weapon's transformative capabilities, in tandem with each other and her Semblance in order to maintain an edge over her opponent. Basically every named character is around this level of skill in the early seasons.
Now for Velvet. Velvet is able to perfectly and instantly mimic the exact moves that she observes other people use in combat as well as utilize multiple different fighting styles simultaneously, both armed and unarmed. Thanks to Anesidora, Velvet is also able to copy fighting styles that utilize weapons, and she is able to wield the weapons that she copies just as effectively as their original user. To date that we know of, Velvet is able to simultaneously utilize the fighting styles and weapons of Ruby Rose, Yang Xiao Long, Weiss Schnee, Blake Belladonna, Nora Valkyrie, Sun Wukong, Penny Polendina, Coco Adel, Peter Port, Reese Chloris, Fox Alistar, Vega Bleu, Yatsuhashi Daichi, Russel Thrush, Roy Stallion, Neptune Vasilias, Brawnz Ni, Bartholomew Oobleck, Flynt Coal, Edward Caspian, and Scarlet David. Of note, every person listed spent their entire lives training in combat and several of them are professional huntsmen with decades of combat experience. Moving up the chain we have Nebula Violette, who not only outmatched Velvet in a 1v1 test of martial arts skill, but was directly stated to be more skilled than Velvet in combat despite Velvet mixing numerous fighting styles to try to throw her off in their fight.
Then theres Mercury. Mercury is a veritable master of close combat, having spent his entire life training in pure martial combat to make up for his Semblance being stolen by his father. He is shown to be a very acrobatic and agile fighter who relies upon quickly overpowering his opponent with complex kicks that imply a near-mastery of martial arts that resemble Tae-Kwon-Do. He is also capable of a break-dancing style, similar to Capoeira, and makes use of Muay Thai as well. Despite his focus on kicks, Mercury also uses his hands to grapple, block or redirect enemy attacks. His experience and skill are aggressive and effective enough to drive even fighters of a high caliber, like Pyrrha, into a defensive position, with Word of God confirming that Mercury would defeat her if he fought her seriously. Due to his fighting style, Mercury relies on his swift and quick reflexes to counter and block his opponent's attacks as first demonstrated during his fight with Yang Xiao Long, altering the course of her punches and using his footwork to raise her fists and kick underneath or around her attacks. Despite the presumed awkwardness of his weapon's ranged capabilities he is a skilled marksman, able to shoot a phone out of a person's hand from a good distance away, and is proficient at using the many different forms of projectiles at his disposal to keep his opponents off balance. Mercury is also known to be observant, tactical, and analytical, able to notice and deduce the capabilities and limits of Pyrrha's Polarity Semblance after she uses it once during their brief fight, despite Pyrrha using it extremely subtly in combat and having spent her entire life honing her ability to hide her Semblance and its mechanics from her opponents and the general public. Of note, both Cinder Fall and Emerald Sustrai are equal to Mercury in skill, and Post-Haven Team RWBY are on that level as well.
Adam is skilled to the point that Cinder, Mercury, and Emerald as a team were afraid to face him in a 3v1 fight and opted to obtain the Maiden powers before challenging him, and he casually stomped both Yang and Blake individually and took both of them on casually together.
