Not sure how anyone is taking Saturn's comment to Kizaru as an insult. It is very clearl he's been conflicted about hurting Sentoumaru, Bonney and VP the last 5 chapters.
Saturn calling him "unusually slow" just lends credence that Luffy only hit him because he is conflicted and distracted. Yes, Kizaru is 100% a glass canon and cant take hits like Kaido, but that does not mean he's been remotely going all out.
Repeating myself, but there is 100% a reason Oda has stalled their fight. A big Flashback, among other things, needs to happen first, and its VERY likely Saturn alleviates Kizaru of the position of killing VP.
This will allow Kizaru to fight properly later on with Luffy.