Seriously, this fight is disappointing.
Several chapters ago (ch18-19), we had a fight against a much lower-level opponent with a restriction that more-or-less gave them equal chances. (3 hits to win, regardless of actual damage. An opponent with multiple special skills.) There, MC learned how to fight smart, not relying on overwhelming difference in stats, but actually using observation and strategy.
Here, we have an opponent of still much lower level (though the difference was narrower), one skill to equalize their base stats and a single special skill. A pretty obvious one at that. It should have been an easier fight than the previous one overall, but it got resolved by dropping the smart approach that he learned before and relying on a new skill to get back the overwhelming strength difference and brute-force the rest of the fight. At the sacrifice of all his levels.
This is dumb. This is not character progression, it's regression. And I don't mean this about his levels. (Which he can likely get back pretty quickly thanks to his other levelling cheat of "1,000 times xp".)
It's just a way for the author to reset his levels because he wants the story to go this way despite the fact that it's a straight counter to what was shown before. I hate this kind of forced story development.
And all this for a character that got from bullied to bully... or even straight-up serial killer... when he got his wish for infinite levelling. (A pretty common trope.) This didn't even bring much character development to the MC, just the simple summarization of something he had already realized before: that connecting with people is not a thing to run away from.
So, dumb fight, negative progress in fighting skills, and zero character development.
In terms of narration, it's a pure waste of a few chapters.
There was opportunity for character development, but it came way too late. This all would have made much more sense a few sections back. While he was still doubting himself. Or while he was still brute-forcing his fights. Preferably both.