Here is the thing, Oda has Luffy "reacting'' to Loki and Kizaru to signify to the reader that Admirals are strong and a threat to the Yonko.
Before Luffy became a top tier we already knew that his opponents were strong but now that he became one for the average reader who read Marineford they wouldnt think Admirals are a threat, thus he had Luffy react and says Kizaru is strong to establish that for them.
The same is now done for Loki, Luffy is a top tier and once again he has to specify that Loki is strong for us the readers to scale him.
I hope it makes sense to you and you understand it lol. Not everything is about powerlevels.
Before Luffy became a top tier we already knew that his opponents were strong but now that he became one for the average reader who read Marineford they wouldnt think Admirals are a threat, thus he had Luffy react and says Kizaru is strong to establish that for them.
The same is now done for Loki, Luffy is a top tier and once again he has to specify that Loki is strong for us the readers to scale him.
I hope it makes sense to you and you understand it lol. Not everything is about powerlevels.
Lol, luffy's reaction to kizaru was not for himself, luffy can protect himself but the rest of the crew can't resist him, his reaction was not fear but concern for his friends.