In order of most blessed to less.
1. Luffy. A no brainer. Pretty much the strongest Mythological Zoan that allows him to literally do whatever the author wants. Member of the D clan and part of the Monkey family which is also significant because his own father is the most well known criminal rn and his grandfa is basically the hero of the Marines, fighting face to face with the PK himself. Plus CoC.
2. Number two, Daddy's experiment. Granted abnormal stats, heat resistance and even a power ranger suit only because he was born. Actually, did we even see Sanji training even once? Like damn, Judge the goat. And for those saying that his modifications only appeared in Wano, check your facts because Oda himself stated that Sanji had an abnormal level of heat resistance from the beginning. Basically, what's needed to use his main power up; Diable Jambe. Now, we don't know if Judge also gave him DJ itself somehow but at this point I already expect something like that. It's a shame that him and his royal family are a bunch of frauds that lack any kingly ambition.
3. Zoro. We've seen him training since day one, non stop and he is also the only guy that Oda showed us training several times without being a training "session" in OP. Removing the fact thay he has CoC; which is there only thanks to the fact that he has kingly ambitions and the will to stand above the rest (same could be said to Luffy ig but we are yet to see if his father has it), he has nothing else special. No op devil fruits nor parents to genetically modify him. He comes from a family of pretty much fodders, being basically the only relevant Roronoa. The only "special" thing he might have is that his ancestor from like centuries ago was Ryuma himself. Which may sound op until you realize that centuries after Ryuma's death, no other Shimotsuki became relevant again. Quickily thingily; being someone's son doesn't even mean that you will end up being important let alone strong (Ace for the important part and Big Mom's half a million sons and daughters who are fodder) now, if being someone's child doesn't grant you direct access to that, why would someone who descended from someone who died centuries ago and whom you weren't even directly related till 2 generations ago when your granda married a random girl from Ryuma's clan.
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Why wouldn't the D Clan blood also decline?
They would also decline, however; we met more important D clan members in the present than important Shimotsuki's in several centuries.
1 Shimotsuki Ryuma vs D.Luffy, D.Garp, D.Dragon, D.Law, D.Teach, D.Saul, D.Ace, D.Roger, D.Rouge and D.Xebec. All of those being at most, 2 generations apart from each other.