Skill list for Archaon would be firstly before any amps or even completing his training, he was skilled enough to fight off the entire Altdorf garrison regiments ( even if it wasn't the entire city's garrison, the city was placed on high alert for attacks, at minimum this would have been thousands of soldiers), as well as the entirety of two knightly orders, who at the time would have been just as trained as equipped as him as one of said knightly orders was the one who specifically trained him and taught him everything he knew at the time, it was a force large enough to be described as a "sea of steel", all the while his soul and body was being burned by Sigmar's holy power, and the only reasonable response the Empire had to even attempt to take him down at this point was to sacrifice the entire temple and bring it down on top of him with magic and artillery fire.
He would then travel north, taking his time to master every weapon and form of combat he came across to know every strength and weakness of them so they couldn't catch him unawares. He killed every single challenger who came across him, always learning and improving. Eventually he ended up in the Altar of Ultimate Darkness, where stripped naked, losing his sword, and being completely blinded both physically and even through his witchsight, he fought off an army of hundreds of giant chaos spawn, literally killing everything in the Black Ark by himself with his bare hands, Doomslayer style.
He would then spend several decades as a pirate, learning everything he could about naval combat and strategy, by this time he has claimed to fought nearly every kind of foe from most nations. When he was betrayed by his allies, he was forced to fight a dozen perfect clones of himself (these clones were so perfect they literally thought they were Archaon) and he dealt with them rather easily. When washing ashore of the Southern Chaos Wastes, he was immediately beset by Beastfiends, which he had to fend off and kill on a daily basis as everything in the Souther Chaos Wastes wished to kill everything it encountered, and he eventually went full Ark Survival Evolved, fashening a outfit of monster hides and a cloak of weapons that he would utilize depending on the situation. This went on for weeks until he managed to get to the Volcano and fight the spirit of the first Everchosen for his armour, this being only being bested prior by Sigmar himself.
He would eventually fight Ograx the great, an undefeated champion who he was the only one to best, before the two of them teamed up and soloed an army of chaos furies. He would then encounter Be'lakor and to even get close to him he needed to fight off the wraiths of every past Everchosen and every potential Everchosen who had died (this would have had to been DOZENS of comparable foes if not HUNDREDS, he took them all on and was winning before Be'lakor finally deemed him even worthy enough to fight. Be'lakor stomped him in the fight, but it was made incredibly obvious that it was a completely overwhelming power, with Archaon actually being the better fighter even when hopelessly outmatched, with it being driven home that if he was able to even touch Be'lakor he could have dealt some serious damage.
He would then go through the Realm of Chaos and End up in the Northern Chaos Wastes, in the eternal battleground, where countless thousands upon thousands of chaos champions fought each other eternally in hopes of receiving the grace of their gods...he killed so many that eventually they stopped fighting and joining him and encountered another potential Everchosen, who he was physically outmatched but outskilled and outsmarted. He then spent several more decades travelling and honing his skill and strategies against any foe he could find, all the while slaying every challenger to his rule on the daily. The tag team of Ograx and Archaon proceeded to single handedly kill an entire warband of khornate champions who failed him and countless manticores and chimeras on their way to Krakanrok.
He then on his final trials, solo'd another army of chaos furies, navigated the multi-dimensional labyrinth of Tzeentch Blindfolded, and casually fought and singlehandedly strangled a Bloodthirster of Khorne to death (Khorne's greatest champions, genius's of combat and who have witchsight/Low 1-C analytical prediction) and then immediately after fought Be'lakor, this time with both of them relatively even, though because of his skill he was able to finally beat down the Daemon Prince and prove himself Everchosen. Then he proceeded to jumpstart the Endtimes, where he fought Valten (who casually killed Count Mordrek, Wulfrik the Wanderer and several other chaos champions renowned for their combat prowess) and while they were relatively on par, it was very clear Valten was fighting a losing battle and Archaon would have won in the end if it wasn't for a Verminlord kill steal at the last second (******* skaven)
Then he went off and fought Karl Franz and absolutely ******* decimated him, and took on Ungrim Ironfist (this technically ended in a stalemate however since Ungrim exploded but again it was very clear Archaon most likely would have killed him eitherway), this is all also ignoring the fact that even though he is Everchosen, he is still constantly challenged by his followers because they think they are more deserving of being Everchosen. In the end he was recognized that ONLY Sigmar was even remotely capable of hoping to actually taking him down ( a mistake Grimgor obviously made though with surprising leeway until Archaon went full powa) and even when Archaon fought Sigmar, nerfed as he lost the Eye of Sheerian, he was still more skilled and managed to disarm him and WOULD have killed Sigmar if it wasn;t for a last minute distraction via Volkar's sacrifice, and even THEN their fight ended in a stalemate as Sigmar and Archaon were sucked into the Warp portal grappling each other.
this is also ignoring AOS where to even qualify in the lowest branches of his personal army, the Varanguard, you have to be a chaos champion with thousands of years of experience and be renowned as both a leader and warrior, and then go on several gruelling life or death quests, ending in a battle with countless others like yourself until one remains, and then MAYBE you will be worthy enough of a personal inspection by the big man to see if you have what it takes to be a common footsoldier, where you will work up through the ranks for many many many more countless campaigns, with even the greatest cream of the crop of the Varanguard still completely and utterly falling short of Archaon's own capabilities.
In AOS he also took on an entire Stormhost by himself multiple times (Stormhosts are anywhere from hundreds to thousands of Stormcast Eternals) with each Stormcast being a literal legendary hero plucked from their time, amped with Sigmar's power and encased in armour and giving a form of ressurection allowing them to live countless lifetimes in service against the forces of chaos, and Archaon on multiple occassions (atleast twice on screen, but several more times have been stated off screen) just straight up rushed headlong into them and slaughtered them like helpless children consistently, and on several occassion fought Sigmar himself head on with every encounter ending in either a stalemate or Archaon decisively winning, like when he fought the combined armies and might of Sigmar, Teclis, and Gorkamorka (the combined orcish/urruk gods Gork and Mork) and utterly humiliated them martially and strategically, leading to Order's worst recorded defeat where Sigmar even lost his prized weapon Ghal Maraz.
Wulfrik the Wanderer would scale in skill to characters like Sigvald the Magnificient who dedicated himself to the perfection of sword fighting, where he was causally able to kill hundreds of khornate champions by himself, each champion having spent centuries honing their combat prowess as their only true desire, and being vastly superior to the likes of Swordsmasters of Hoeth, who have hundreds to thousands of years of training, and are so skilled with the sword they are capable of individually killing thousands of other elves who have hundreds to thousands of years worth of experience themselves, all the while simultanously deflecting dozens of arrows from the air, and choking entire rivers with bodies, with Swordsmasters being compared to children when against the likes of Malekith and Tyrion who are capable of killing hundreds of swordsmasters singlehandedly, these characters again completely all falling short to Archaon.