Sure, this i can see, but I think at this point in the ballgame its very hard to justify Luffy losing when his main competitors for One Piece just defeated his other rivals. If he loses here (not talking about a round 1 stomp), it just sets back this story potentially years lol
Oda always has Luffy get his major victories in 1v1s. If Luffy can beat Kizaru right now, or Saturn if he's as storng as Kizaru, and Kizaru is close to Akainu, Luffy is either as strong or nearly as strong as the Marine Fleet Admiral, going to Laugh Tale.
Surely you can see why this breaks One Piece's power scaling?
Luffy will surpass Admiral level soon (around Elbaf probably) then Yonkou level when he beats Blackbeard at Laugh Tale (with Blackbeard beating Shanks to hype Teach up).
Luffy can fight Admiral/Yonkou level fighters for a bit now, and damage them.
If he 1v1s Kizaru, and he uses Gear 5, what's happening during it's cool down? Luffy just dies, man. Ain't no Brulee sticking her head out of a mirror to save Luffy from the speed of light.