They keep adding more characters to 4 and not a single new map when its biggest flaw is that it doesn't cover more arcs and barely has any maps and most maps it has suck with annoying backtracking and corridors

3 covers the entire manga (down to smaller arcs like Loguetown), has all the characters you could want from the start, better map design and NPC behavior so that there is actually some strategy involved (in 4 your NPC soldiers and allies are pretty much broken and don't do shit), and it has better dodge mechanics and dodge offset, something 4 for some reason got rid of, which actually makes it clunkier than 3 even though it tries to be more fluid

The supposedly good additions in 4 are jumping, which is actually pretty pointless in this type of game, and the class system, which is also pointless in this type of game and just imbalanced and sucks