Punk Rotten is several times bigger than Kaido or G4 Luffy:
These slashes were taller than Punk Rotten:
The slash was way larger than Zoro when it's coming towards him but it looked smaller as it traveled further away from him. And the same thing happened to the slash that Luffy blocked(bottom right):
They even sliced off a similar-sized rock.
Demolition Breath isn't a focused attack: He violently sends slashes in all directions. All the slashes would come at Luffy if the attack was completely focused on Luffy. It's the same shit he used in 1003 with the only difference being that Luffy's the only one fighting Kaido in this chapter.