Negi would recognize Asta's antimagic as Asuna has like 90% of Asta powerkit
Second: Negi whole power system is magical mixed with a bit of chi, but even the chi part is considered "Eastern magic" and is more like using Zetten to boost certain spells, but they still used mana, his regen is countered by Asta, even if he uses Cassiopeia, Asta resist time magic and this Asta has a passive antimagic forcefield that completely nulls Negi spells and even then, antimagic skin, this is ignoring how Asta would deflect his attacks
Ap: Asta has more AP, but is 1.16 times more of less so meh
Speed: Negi can become 3.6 times faster with his form, Asta if using Zetten from base is speed blitzing and by lore he is 10-20 times faster than his base, add his transformations and Negi can't react
Hax: Negi has more hax but antimagic counters him, Asta compared to Asuna, while Asuna can fight someone with 700 years of experience in battle and who is a master of 3 martial arts, Asta can learn how to use a sword in 1 week to 1 month (Fanzel novel which I can't found in my language) and learn techniques mid fight, Negi is superior to Asuna and Asuna has a few weaknesses in her antimagic like being weak to illusions, ingering magical food still cause her (but not to the 100%) symptons and using magic on her insides affects her way more than targeting her skin, while Asta can dispel inside effects and would not be affected by illusions for the antimagic barrier/skin+ being able to dispel them, I won't cover his summons
Martial arts/combat: Negi is extremely good and is better than the girl with 700 years of experience, probably better than Jack Rakan (and superior to him in the spin off series for sure) and is an expert at training and developing spells and improving his combat style, Asta you just have to read his intelligence to see that he matchets Negi or at worst is a bit inferior (and sorry but I don't know what skill feats I can bring for Negi but while Asta learns how to use a sword in weeks, Negi learns a martial art in hours for example) the thing is that Asta has way more "passives" that makes the skill debate turns in his favor, as he would adapt, would grow stronger and has precog, negi has precog too but is way way inferior ()
How the fight should go: Asta starts with zetten, Negi sensing no magic and recognizing antimagic SHOULD, use illusions, as that is his counter for knowing asuna, the only user of antimagic
If a Zetten strike does not nullify his regen as he needs to use third sword, the next strike will surely do, while Negi is out of options, clones are magical and will be nullified and Negi vs Asuna comes to Negi countering her with superior combat prowess and said illusions, Asta has almost equal combat prowess but is way faster and not affected by that
Asta low to mid difficulty, if you want to see it as a stomp, I don't mind