One Piece is a better manga than KnY, HxH, and MHA. The reason why? Here you go.
One Piece has no asspulls. The other three series are loaded with them such as:
HxH
>O MY RUBBER NEN
>alluka/nanika
>Emperor time
>Gon San
KnY
>O MY FLAMING SWORD OF FLASHBACK
>O I CUT MY OWN HEAD OFF WITH MY WEBS
>O MY BUTTERFLY TOXINS
MHA
>O MY SEVEN QUIRKS
>O MY ERI POWERUP
>O MY ALL MIGHT
One piece also has infinitely better worldbuilding than the other three series. HxH takes place in an ancap wasteland that looks like a bizarro version of America thats surrounded by a boring unexplored spooky continent, KnY takes places in a boring Japanese Feudal society of the 1800s, and MHA takes place in a city mostly. One Piece has a new theme every arc which keeps it fresh. One Piece also has a better plot and theme to it unlike the other three.
KnY, HxH, and MHA are trash, Face it.