First of all I have to inform you that you don't have slightest idea what logic is what can an what can't be called logical.
One Piece doesn't have problems with logic, it just contradicts common experience - which is what fantasy story in fantasy universe is supposed to do.
One Piece has inner logic. Stuff only works in certain ways, not the others. Mechanisms from our world not necessaries work in One Piece world, albeit some of the of them work in similar way.
Problem is we don't know how many of mechanisms (like social mechanisms, natural mechanisms) works there in symmetrical way to our world, so estimations are hard to do.
Other problem is we don't know that much of the setting to make elaborated predictions (apart from knowledge of mechanism - knowledge of the rules, one must also know parameters of the setting to make predictions).
Well, maybe I am using bad words to describe my thoughts. I will not comment on what logic is and who is right or wrong, since I want to contribute to the topic itself, rather than to create a dispute. What I mean is that there is no certainity in this manga, there are no rules or inner logic the way you describe it. Blackbeard is a great example, you are told many years that no one in the world can have two devil fruit powers, but then Blackbeard shows up and he can do it. Of course there will be some back story created and some new laws or rules to back it up, but that is my whole point. Nothing is certain in here, Oda can always figure something out to make something from few years old episode no longer valid. So like I said before, anything goes. That is why I think it is wierd to look for any decent explanations. Oda might as well make Luffy eat 3 devil fruits if it will suit the story needs, and he will always make some crazy explanation that will fit into current system of rules.
I am pretty confident that many of the stuff that is a explained now in manga, were not in plans since first part. He just reads back his own stuff and looks for characters and stories that he might bring back with a twist. It is not like he has a master plan since day one. He can come up with anything, and you will think.. oh… so that is why 10 years ago they did that.... but 10 years ago he had no idea it will turn out like that, he just saw that possibility now. That would be what genius does.