The obsession with Kiryu's parents makes no sense to me. If there is one theme that runs through every single one of these games, it's that the bonds you choose are your real family. The subject of who Kiryu's real parents are comes up very rarely and when it does Kiryu could not be more explicit about the fact that it doesn't matter to him, because Kazama was his real father and the Sunflower orphans his real siblings. So why have so many people latched onto this idea with so much excitement? Even putting aside the fact that it would require Daito to be having kids in his twilight years and Kazama would have to kill him (or become a liar with a terrible retcon), Kiryu's genetic parents have always been explicitly unimportant and I don't get the hype around this now.
The obsession with this subject really feels like it's driven by people who just haven't actually played these games or absorbed the messages. I know Yakuza's writing can be obtuse at times but this is really not one of those times.