Whether it was croc
Katakuri
Or kaido the whole point of those fights were for luffy to surpass them. Sure you can argue that when they return they come back stronger than their previous selves
- Luffy left alabasta stronger or at worst equal than alabasta crocodile
- Luffy left wci stronger or at worst equal than wci katakuri
- Luffy left wano stronger or at worst equal than wano kaido
Lucci is a similar situation but in this case luffy gained the power to do so before their fight aka gears. Tho obviously he had to push himself to his limits still to surpass him
There are exceptions tho with obviously opponents he doesn’t defeat at all but also Enel. Enel was way stronger than luffy overall but luffy just happened to be the perfect counter
As for cracker and Doflamingo they weren’t significantly stronger or at all stronger than luffy. At worst being on a comparable level and within reach of luffy