Hold on, I thought this was just having them both at their peaks? As in Chapter 12 Asuna and having Nora start at 300% to make things even. 8-A and MHS+ Isn't something Asuna reaches with amps, it's the level she's already achieved which is why it's put as "Eventually became". I don't think this'll affect the match too much, though.
As problematic as that may sound, many demons in path of wills have reaches significantly greater than that with their physical size alone, which Asuna has been dealing with even before she could effectively use Soul Energy beyond increasing her physical strength. Facing something massively larger than her isn't anything new. It's also explicitly stated that Nora has little combat experience in her weaknesses section despite her inhuman way to move her joints, so the size of her weapon isn't an advantage she can use to it's full potential from the sounds of it.
Of course, as mentioned on discord, Asuna's skill is also superhuman in it's own way, and she has far more feats of this sort of thing from what I can tell. Plus, her own adaptability also shouldn't be underestimated either. Nora can increase her strength with amps, but Asuna can evolve in response, starting from a value she already upscales. Nora is said to have potentially "Lethal" side-effects when using her amps too, which doesn't sound great for her. It's not explicitly said what these actually are, though, which I think should be updated on the page
How does Nora use her overthinking ability in a fight? Who has she beaten with it? All of her intelligence feats seem more related to processing speed, innovation, things like that rather than countering things in live combat. And even if she's constantly shifting gears to deal with her opponent, Asuna will be doing the same thing.
Nora's adaptability is akin to machine learning. At the start of the series, Nora starts off completely helpless, and through being put through several life-threatening situations, she becomes somewhat competent at swordsmanship.
The rate of her development is exponentially faster than the rate of an Average Arkane, as she was engineered to be "superhuman," superhuman in Ark terms would translate to well above average.
What kickstarted Nora's progression is her spar with MEGA. Throughout the spar, Nora was unable to land a hit on MEGA, having each of her attacks dissected and countered. MEGA, having already surpassed the combined efforts of mankind in the art of swordsmanship, became an immediate hurdle for Nora to overcome, allowing her to grasp the fundamentals of swordsmanship and to soon build a foundation for her future victories to come. Nora's growth was evident in her next spar with Almace Alcatraz. Nora was able to adapt to Almace's acrobatics:
A talent that allowed her to twist and turn her body in impossible ways to gain leverage in the air & even invert the direction of gravity, allowing her to perform double and even triple jumps.
Nora's adaptability even allows her to incorporate concepts into her own arsenal. Going back to Almace's acrobatics, she is so adept at acrobatics that she is capable of redirecting the momentum in her body to change her velocity. Nora found that out the hard way, and through the annoying feline's constant evasion, Nora was able to incorporate this momentum distribution into her fighting style.
Nora was also able to learn how to fight against instinctive reaction through the same spar with Almace Alcatraz. Almace is a nekomata with the following type of instinctive reaction:
Nekomata can intuitively dodge attacks the moment they sense them—relying on animalistic instinct rather than conscious thought. It is so effective that the commonly accepted notion is that nekomata will always certainly dodge the first two attacks you try against them—even if they had no prior awareness that someone was even nearby. Once they've seen an attack once before, their body will naturally learn the patterns of movement needed to evade it going forward, executing them instinctively every next time they're utilized.
The conditions of the spar between Almace and Nora are that Nora would be declared the victor if she could land three consecutive hits on Almace. The fight had a time limit of five minutes, and she managed to hit her all three times within the last minute. Within the span of four minutes, Nora managed to garner enough skill to outdo the natural skill of Arkane Nekomatas.
Overthinking also plays a role in this. During the spar, Nora was unable to hit Almace for four minutes straight, causing her to become stressed and embarrassed about the situation. Throughout the match, Nora kept on thinking about the situation, how she was not good enough, how she wished she were stronger, and overall had a plethora of thoughts about how she wished she were better. This drove her desire to "land a hit" to an all-time high, thus increasing her ID. As I mentioned, this increase in ID plays into her ability, specifically her minor probability manipulation. The higher her ID is, the stronger she becomes and the more likely she is to warp the probability of the world around her to get her way.
Not only did Nora get stronger, faster, and more skilled, but she also increased the probability of her desires happening, all because she kept thinking about it and raising her ID.
The longer the match takes, the harder it becomes for Asuna.