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
That's 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 there's 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.