No? Sanji and Kuma are also confirmed PoL users. Likely many more including the Ds
Kuma didn't hurt Saturn like Gaban did,
Nor did Sanji with Venus,
Fist of Love refers to Garp disciplining those He loves, that's why He said it cannot be blocked,
Haki is Willpower & each person is different, everyone have a different Motivation, and different emotion that empowers their Will,
You're acting as if this Love is something Unique,
Haven't you seen Usopp fueled by Bravery against Perona?
Haven't you seen what Luffy just turned into? A Being fueled by Laughter & Joy?
Haven't you seen what happened to Zoro when He is at Death's Door?
Haven't you seen how Jinbe reacted to Who's Who Words?
Haven't you seen how Kaidou's Haki grew Stronger when He was Drunk or when He lost Big Mom?
It's like Haki is Flames, and each Character burns different stuff to make it, it doesn't mean We create a New Power-System for each Character depending on which Emotion motivates them more