There Are Better Character Dynamics
As established earlier, now that we know who Lara Jean and Peter Kavinsky are as people, To All The Boys 2 (which should have been called 2 All The Boys, for the record), allows the characters to interact and communicate with each other in more sincere, believable ways. Additionally, whenever John Ambrose enters the scene, the ways in which they intertwine with their personal backstories is more investing than the romantic triangle between Lara Jean, Peter Kavinsky, and Josh Sanderson, where Lara Jean was the only real, honest connection between these three characters. This time around, it is apparent that these three characters have a history together, outside of their romantic relationships, and it makes the dynamics found between them more investing to watch. There are more stakes in place, and you believe that Lara would both want to stay with Peter AND get together with John too.