Well, the difference is that KAIDO as a villain will not succeed because he is not the protagonist.
I will explain why, ODA said in an SBS that AKAINU would find the unique piece in 1 year, akainu as an admiral, already in "AUGE", luffy started from 0, without HAKI, weak and stupid, in just 2 years LUFY is one step closer to being PK, in just 2 years and he started from 0, according to KAIDO whoever wins will be just 1 step away from becoming PK.
Returning, AKAINU, in 1 year it would become PK, but we have a fact that KAIDO is stronger than AKAINU, so what prevents someone more powerful than AKAINU from finding the unique piece before Luffy and in less than 1 year?
Answers: It is not the protagonist.
The answer is simple, for the fact that AKAINU becomes PK, because AKAINU is a scenario like him being the protagonist of the manga, you need to learn to separate these two things, the term protagonist makes a big difference here, so don't show me the privileges of being a protagonist as something to boast about.