I still don't understand the mention to wife #8 and how that was ironic. At least we know the sapphire scales was caused by Saturn's human experiments rather than it being a sexual disease of some kind.

Saturn orchestrating everything is still in character. We still don't know why Kuma's race was almost eliminated but I think Saturn has a special hatred for Kuma. Saturn keeps referring to other humans as "insects" so buccaneers defy that chauvinist thinking as Kuma nearly rivals Saturn in size. Him being involved in Kuma's life and eventual death goes back to his obsession with power and attempting to erase any threat to the power dynamic.

Same goes for Kaido and King, if Saturn truly is just a human, then both Kaido and King are also threats to Saturn's image of essentialist dominance. Maybe another detail to why Kaido's crew is called The Beast Pirates. The WG wants to dehumanize them at the very least if they can't destroy them. Similar to why the Gorosei and Celestial Dragons enslaved Kuma instead of eliminating him completely, they can't show even a hint of fear/weakness.

TL;DR: It's more like, Saturn's own selfish humanity was what caused his downfall.