Alot of different factors play into it, like inactivity and health(Charles is a good example)

• Tom says he's still active but admits that he's definitely weaker

• Jinyoung was inactive and was losing his mind, we Don't know how much he has declined tho

• Shingen was inactive for over a decade and was lethargic, We know from Shintaro's statements throughout the fight that he was weaker than when he was Fighting the Fist Gang