Something minor I've noticed only a couple times in the Yakuza series. Majima being "CEO of Majima Construction" when you encounter him for the first time in yakuza 2, but being "Patriarch of the Majima Family" when he fights Kriyu in the arena. I think Kiryu just being "Ex-Tojo Clan Fourth Chairman" as well as how he uses like 1/10th of his moveset is a great indicator of how much he's holding back. I think one day, be it in the next game or 5 games from now, Ichiban will fight Kiryu with the dynamic intro "Kazuma Kiryu, The Dragon of Dojima" when he's finally able to fight Kriyu as an equal.
Kiryu could have destroyed them all easily, the way he effortlessly took that punch to the head without batting an eye confirms it. Kasuga's got a long way to go but I think he'll end up matching Kiryu in terms of strength. Kiryu is basically a raid boss.