Omori clarifies a lot in this prequel. Whether it's satisfactory or not is another thing but it does a lot of explaining I feel regardless should've been earlier
It explains the basis of the magical world, the magic system that was sorely lacking in explanation until now, like the elements that people use, and how one element per person was generally the limit, which is why even prodigies like Elfaria just cant do everything possible. There are exceptions like Multos(or people who can use multiple elements) or people who have an affinity to the ultimate rare magic of light magic.
The characters Will and Elfaria's relationship is explained in very through detail throughout both of their POVs, making their entire relationship in the novel and manga come a lot more smoothly and understandable once we go through it all. It's revealed Elfaria did not go to the Tower willingly at first, as she intended to stay with Will forever, but due to one of the Magia Vende's nearing death and the reveal of her talent that she tried to hide from the public, the other Magia Vende effectively forced her into the role.
Will's ridiculous physical stats? Yeah that's not him working hard or never give up bullshit. He was blessed with that from the very start. To the point where he could break bricks even as a baby. The later manga chapters clarify that Will's magical energy keeps stocking up in his body and he cannot release magic through any other way outside of using Wis. The Light Novel clarfies that the magical energy he keeps building up and stocking up, is amplifying his physical parameters to a level ridiculous for a human. Will does train, but thats more to learn how to use the sword rather than helping his physical stats, since they're already monstrous even when he was 10 years old.
To put in perspective, Will's physical abilties were so good that he was already gathering far more "practical" (actual combat in Dungeon) credits than all the other first year students according to Workner by a large margin.
Will's physical amplified abilities do however come with a cost. In the early manga chapters of Wistoria there's a few joke scenes about Will working too hard and having his hair growing whiter due to stress. The Light Novel clarifies that is the sign Will is using his abilities too much, and it starts removing his inner self and memories the whiter his hair gets. Will would lose a bit of his memories just using the magical energy he had inside of him with Wis, and if he used the real Wis, he would become completely amnesiac. The first time he used Wis according to the manga chapter 36 or something, he beat the enemy sure, but the LN covers the scene after where he became completely amnesiac as a result and forgot Elfaria and himself entirely. That realization broke Elfaria, and their adopted father used a hypnotic magic to forcefully give Will records of his past from the father's view to keep Will from completely forgetting. But any memory that the father did not have of Will, Will lost permanently that day.
With one exception.
The promise mentioned at the start of Wistoria and is the premise of the entire story. That's Will's one "true" memory that hasn't been deleted or given to him through a suggestion and it's the only thing he feels strongly about when he looks at his past memories. So basically Omori divulged the real reason why the childhood promise scene mattered. Elfaria who later found this out as well sobbed and decided she would definetly see the sunset with Will and find a way to repair Will's memories no matter the cost. When they became students, she repeatedly broke into the forbidden libraries of the Academy with her clones, to try and find secret documents relating how to repair memories with magic. She became stupidly overprotective of him after the incident where Will used Wis, and made sure she could handle anything that came near him, because if Will fought, even if he won, he would lose memories of her and she was terrified of the idea. She helped Will hide the fact he was an incompetent, by giving him a necklace with her magical power in it, and decieved the eyes of the Academy by channeling her power in it, so everyone, even Will thought he could use magic when he enrolled in the Academy. It however did get exposed later in the Light Novel.
At the end of the Light Novel, Will uses his Wis at full power to defeat the enemy, and as a result, completely destroys his memories on an even harder level than before, and only referred to himself as a "Sword" because his Wis turning him white/silver is a sign he's becoming more "Sword" than human. The principal arrives too late, to see Elfaria sobbing and Will mentally dead, and uses the magic she used on Will on the manga to try and restore him. It wasn't perfect, but it was enough to restore Will back to the state he was at the start of the LN. Apparently the principal's magic is good enough to remove the memory backlash of Will using his physical abilties normally, but she wasn't good enough to restore his memories once Will actually used Wis. Knowing that The principal noted, Will's body was still far too young to handle the power of Wis, decided to make a deal with Elfaria. If Elfaria properly became a Magia Vende and became a "goal" for Will, the principal promised to eventually repair Will's memories and raise Will in the Academy where he could eventually grow and handle the power of Wis. Hearing her terms Elfaria agreed, and left Will to her. And then the end of the LN comes where Will and Elfaria seperate and they once more promise to meet with Will saying he would reach where she was one day, and Elfaria, although not wanting to shackle down Will anymore, cried and smiled and promised she would wait for him always.
And that's the end of the LN. It's implied there will be more LNs with Will's time at the academy with the other characters in the manga that we've known up to now. Due to Wis backlash(plot) Omori can always just say Will forgot whenever something doesnt match up from Will's POV in the manga when he talks about his past. The next arc is implied to be how Will and Colette from how the LN left off as Colette is still an unresolved plot point that the LN started and didnt finish.