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.
Thats the baseline for skill in the verse.
Before the Beacon Arc Ruby had been personally trained by Qrow in combat and as a result she was noted as always excelling above her peers in combat training. At the start of the series Ruby was at a level of skill 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. 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.
Above her is Pyrrha Nikos, the skill god of the Beacon Arc. Pyrrha is one of the most skilled students at Beacon Academy, having won every combat tournament she has entered since she was a pre-teen due to both her mastery of combat and mastery of her semblance, being able to apply it in combat completely undetected and having done so in almost every fight she's been in for over a decade, doing so with such skill and precision that she has lead many to believe she is untouchable and invincible as no one has been able to even land a blow on her in her combat career. Even without her semblance she has shown the ability to quickly and easily adapt to her combat situation and analyze her opponents while fighting and changing tactics to suit the situation she is in. She has shown extreme accuracy, being able to hit moving targets from hundreds of meters away and strike vital weak points on an opponent mid-combat both with and without the aid of her semblance. She is also highly skilled at using her weapon's multiple forms in combat, being able to switch between forms several times in rapid succession to both deliver rapid attacks and counter others simultaneously.
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.
Theres also Neo. Having been trained in the art of infiltration and assassination at Lady Browning’s Preparatory Academy For Girls, a covert school which trains some of the most elite female spies and assassins in the world, Neo is extraordinarily skilled in combat. Her fighting style is highly evasive, focusing on dodging, deflecting or maneuvering around her opponent's strikes until she has exhausted them, or until she is ready for a counterattack. She is very acrobatic and exceptionally skilled in hand-to-hand combat, relying on her agility to dodge and misdirect enemy movements and attacks, before retaliating with her own attacks resembling a mix of Bartitsu, Fencing, and Capoeira. Her skill is such that she casually defeated opponents such as Yang and Ruby early in the series and later on the entirety of Atlas Arc Team JNR and Oscar while toying with them the entire time, and by the end of the arc taking on both Ruby and Blake simultaneously and largely keeping them on the defensive. By word of God, Neo's skill is sufficient to defeat Mercury Black in a one on one fight.
Then there's the Ace Ops. For reference, Atlas Academy's vetting process is canonically more strict than Beacon's due to it being a military school on top of a Huntsman academy, so they only accept the best of the best. All of the members of the Ace Ops graduated top of their class from Atlas Academy, meaning that they are quite literally the best of the best of the best. Ruby not only outmatched Harriet Bree, but scales to the rest of her team in skill who also outmatched members of the Ace ops, Elm in particular being canonically the most skilled person out of all the ace ops, with Clover being the only member ranked above her in combat solely due to his semblance rather than outright skill, and Yang outmatched her in combat. Included in this group is also Winter, who spent her entire military career training to be the replacement host of the Winter Maiden and even without the Maiden Powers is considered the most skilled soldier in the Atlas Military.
Qrow scales above all of this, to the point that he can casually match Winter fighting against him seriously while he is drunk and holding back by not using his strongest weaponry or fighting style, Mercury is outright scared to fight him, James Ironwood (who is able to easily outmatch Winter in 1v1 combat and required the combined efforts of Winter, Team JNR, Oscar, and Emerald to take down) is wary of fighting him one on one, and he can match Tyrian Callows (a member of Salem's inner circle who has personally hunted down and killed hundreds of professional huntsmen)
