He's a prime example of a shit character yet being praised for the thing that makes him shit.
He has 1 thing going about his character and it is praising Kid and telling how great Kid is. He's just another ass licker.
But the problem is we don't know why he views Kid the way he does, or why he chose to follow Kid over anyone else. We just have to listen to his endless Kid cock sucking without hearing anything meaningful.
In short, Killer is not a character, he's just a device to try to praise Kid to the reader but fail miserably.
Also, I never thought I would see something worse than a swordsman choreography fight in this manga, but Killer's fighting style takes it. It has even more nonsensical teleportation than even Zoro's sword attacks.