Much as Gojo is the peak of Jujutsu sorcery, these series collectively represent near perfection, achieving what few if any battle shounen have ever accomplished. I've identified three key factors in what makes them so special.
Pacing
The first key factor is the utra fast pacing. Both series dont take long to reach climaxes. Other shounen take dozens, if not hundreds of chapters to reach something unique and amazing. Jujutsu Kaisen does it within ten episodes through the school shooting arc and first fight with Mahito. Chainsaw man likewise hits deep feelings early on, as soon as the katana man arc hits.
2. Meaningful Writing: Each page, fight, character moment, adds to the story themes, characters and emotion. A story like Black Clover has some of those moments, but also a lot of repetive fights/dialogue that doesn't add anything. JJK and CSM have none of that. If the fight exists, it adds substantially to the story. The reputation of "dumb shounen" comes from stories where action is the only selling point. But truly special stories have great action and writing where everything is meaningful, no repetitive dialogue a hundred times
3. Nothing held back: Both throw extreme violence at the reader, twists and turns and deaths that no other shounen dares touch. One Piece is scared to kill a single character, Chainsaw man and JJK do it with such a perfect frequency that there are constant emotional stakes. But it's never arbitrary or cheap either.
