It's not about strength tho, you have both Portgas D. Rouge and Jaguar D. Saul, it's about the perseverance and determination, also the smiling / laughing shit, Law really doesn't fit this shit too much, not as much as Kidd i would say
Law broke the Gears. Kid was in the New World, he didn’t make headlines. He was just independent. Could he be a D.? If Oda chooses that route, who am I to complain. But Oda doesn’t hand out D cards to just everyone.
So far the carriers of the Will of D shown have had worldwide impacting implications. Kid hasn’t had any although he’s at the height of his Piracy, and has been for five years. Law made massive moves, became a Warlord, broke the Gears, took down Caesar and Doffy, successfully led an alliance with Luffy against Kaido. Kid has rode Luffys coattails in any “definition” of D since Sabaody.