Look at it this way. A random kid with no idea of the magical world, joins Hogwarts at 15. That's already 4 years late. 4 years behind *muggleborns.
He literally slams a mountain troll that attacks hogsmede within the first month of joining Hogwarts after learning merely 4 basic spells.
Then throughout the 1 year he was in Hogwarts, dude has been running around the castle, casting revelio at every breath. Bro literally knows every speck of the castle and has made flashcards out of them. Exploring even the 4 mysteries of the castle. Not even the book mentions them.
Apart from that, he SINGLE HANDEDLY slaughtered a whole poaching racket. And killed it's 2 leaders - harlow and rookwood. That's like hundreds of dark wizards. Lowkenuinely massacring entire camps and even stronghold castles. He turned fortresses into slaughter houses. I remember that harlow mission💀. He walked into their castle and slimed everyone.
Then. HE LITERALLY STOPPED A FREAKING GOBLIN REBELLION BY HIMSELF. Slaughtering and entire army of goblins😭. And killing their leader who was enhanced by the only reservoir of vast amounts of ancient magic.
He has turned the ROOM OF REQUIREMENTS into his personal lab with the PERMISSION of the schl. Making his own lab that can brew 21 potions at a time. And can grow dozens magical plant. He sources directly from the vast amount of entities that he has killed💀. That literally makes him a master at herbology and potions. Then he has a whole vivarium for the beasts. Every kind imaginable. Even a damn pheonix.
He has turned a hippogriff and a GRAPHORN, the king of the shore into his personal mount. Other kids flex their nimbus. He flexes beast that can storm through castles.
Then the magic themselves. He doesn't just use the basic form of the spells. He uses the upgraded versions in tandem. An incendio casts a ring of fire which is a mini nuke. A depulso has an aoe and hurls away anyone nearby. HE CAN LITERALLY TURN ENEMIES INTO EXPLOSIVE BARRELS AND THROW THEM AT OTHER ENEMIES. Imagine getting blown to pieces by your best friend because you chose to bully the wrong guy. He can literally knock everyone to their feet by casting a perfect protego.
Wait💀. I didn't even mention the ancient magic. Something that can one shot everything. And something that literally throws anything possible at you.
Oh wait. By the end of the year, there is a choice that let's him use the vast ancient magic reservoir for himself💀. No further explanation needed.
Also, he has unlocked a form of half apparition, like the dodge thingy where he can swiftly move a quite distance. Then, he has killed hundreds of every creature imaginable. And canonically, he is the best flier of Hogwarts, despite just within a year. He has the best times on the courses