TL;DR: One Piece TCG's official base rarities are Common, Uncommon, Rare, Leader, Super Rare, Secret Rare, and Special, with premium variants layered on top: Alternative Art, Treasure Rare (TR), and Manga Rare (rarest, with very low unpublished odds)
Legacy is not the reason, but the reason is related to why the card is good in Legacy
Otherwise, each creature blocking or blocked by this creature gains first strike until end of turn
These get more play than they should based on their power level alone
And it has myriad for ETB triggers to copy like in color Mulldrifter or smashes like in color beater Deep-Sea Kraken
Combo decks like Azorius Omniscience are something we want to exist in Standard, but when too strong, they warp the format around them and reduce the number of viable decks