Power creep doesn’t just refer to the strength of the verse as a whole subtly increasing over time. In that regard, I think you’re right. One Piece is nothing like Dragon Ball or Naruto.
Power creep can also refer to an individual character becoming more powerful in a way that seems contrived and/or due to plot. In this sense, I think One Piece almost definitely shows signs of power creep. Luffy damaging Kaido with G3 (and potentially no ryou) when just two weeks earlier king organ did nothing is a bit much.
I know, it´s a two aspect concept
1) escalating the power limit further and further
2) elevating relevant characters to that power limit without credible explanations.
It isn´t.
1) The attack has Ryou, it´s a completely new technique, just logically, there is no reason to highlight a new technique after two week training if the first thing he does has no relation to the training at all, makes no sense
2) That´s how Kaido´s power works. He is someone who can ignore physical blows unless they can bypass his scales. This is not an Attack power issue, none of the scabbards have attack power compared to Kong Organ, yet they hurt Kaidou and Luffy didn´t, why? Because they can bypass the scales with AdvCoA.
Meaning if you are a physical fighter and not access to elemental damage, no matter what kind of attack power you have, it´s meaningless. But if you have AdvCoA, now attack power matters, so basically AdvCoA is a prerequisite to fight Kaidou.
Luffy not hurting Kaidou was not because of attack power or lack thereof, but because he did not have AdvCoA, his attacks did not do any damage to the scales, and also were not projected to his insides, but now his attacks are.
We have many characters mention throughout the series that power combinations can be quite curious, one of the most extreme examples being Mr3 vs Magellan. In Kaido´s case, it´s AdvCoA.
That´s for Luffy and Zoro who definitely have AdvCoA.
Law? Goes back to example of Mr3 vs Magellan. BM´s and Kaido´s biggest assets so far have been their durability, now you have a character who can completely ignore durability, also can attack insides with his ability and thus bypass outer layers.
Kid and Killer remain to be seen.
Also, just to point out, fighting Big Mom is just an attack power issue. She has incredible durability but not such a prerequisite of needing to bypass any scales or anything, so if Killer and Kid can provide that attack power, it´s also not lacking credibility. Luffy clashed with her with Kong Gun.