There is absolutely nothing that puts all Yonko on the same level in terms of strength. Yes, Killing WB would earn him more than it does in case of Shanks but the difference isn't much big. I don't get from where you pulled that WB is a level above Shanks thing but manga or anyone else never implied anything like that.
Funny thing is that Kaido should be already above WB as WB is a creature so his title should include WB going by your logic. Yet for some reason you are kinda implying that WB was an exception.Lol
His reason is most likely killing him and take over all of his territories and of course killing WB would increase his reputation. His reasons are irrelevant, Shanks got in his way and tried to stop him from achieving his objective. Given his aggressive nature he would get mad at Shanks for trying to stop him and kill him. By killing Shanks he can take revenge on him for getting in his way and also his reputation will increase but he didn't do that. That says something.
Manga clearly implied that Kaido isn't someone that can be reasoned with, also it seems like you forgot the fact that Yonko are enemies.Lol
Shanks can never offer something that can replace WB's head. But I agree with that point, Shanks most likely offered him something but again we have this Kaido isn't someone that can be reasoned with hype from manga. But still he accepted it or rather he was forced to accept it in exchange for quitting his objective.
I have already addressed that fighting two Yonko argument. Why should he fight two of them again? He intended to take WB's head and Shanks got in his way so he can just kill Shanks and go back to home. It may not be as effective as killing WB but still killing a fellow Yonko means a lot. There is noway in hell for someone as aggressive as Kaido to just quit his objective just because Shanks asked him to. It is a joke if you ask me.
You're oversimplifying things to a ridiculous level. It was never said Kaido wasn't a reasonable person. It was said that when angered, he wasn't open to discussion. However, this does not mean he is never open to making deals. The fact that he had a business deal with Doflamingo and Caesar should he is capable of reason and is capable of making deals. Shanks could have stopped Kaido because of a deal between the two. If you really think that this is completely impossible, then your imagination is pitifully limited.
Defeated a Yonko would make people go "Okay, that guy is Yonko level." Which is highly impressive for someone if you aren't already Yonko level. WB is a level above Shanks because he has the reputation of being the world's strongest man. While a fight between the two would be extreme diff, it simply means that WB's place in the world was higher than anyone else's, thus a level above Shanks. If Kaido could have defeated him, he would take that spot. That is why defeating WB is far greater for reputation than beating Shanks. What's better, beating the person who is number 1 and everyone suspects is stronger than you, or the person everyone already lumps you into the same league with? And no, my interpretation of Kaido's title and assertion of WB's are not contradictory for two reasons.
1. Nami's expression to Kaido's title and Law not denying it insinuates that Kaido is not a human. WB's title as World's Strongest Man could simply mean of human beings, WB was the strongest, but not the strongest of every living thing.
2. This one is far more likely, Kaido was simply called the World's Strongest Thing after WB died. So simple, yet so hard to grasp I imagine.
Kaido wanting WB's territory also doesn't make sense, as there was no indication he went after his territory after WB died. It was said that Teach usurped his old territories for the most part.