Yes, you got a point. Though Luffy in the past has been shown using G4 on fodders to finish things fast. In this case with G5, where Luffy probably used an attack far from his strongest, wasted awakened Lucci, meaning the difference in strength is that big.
The difference isnt that big though.
You forget that even the gigantic dragon form Kaido was thrown left and right by G5 Giant.
The only difference is that Kaido isnt taking much damage from it while Lucci is.
Lucci is stronger than people think. The same would happen to all High tiers if G5 Giant steps on them...
The difference in this specific case is that Oda skipped all the things that he usually shows.
Luffy jobbing, warming up and so on and skipped straight to the end of it.
I guess the usual humiliation Luffy receives will only be doable by top tiers from now on.
Unless he changed his mind on that as well and it is villains who will get Looney Tunes treatment each time.
Shishishi.