NPC probably could better their skills after the Apocalypse. Maybe they just don't know they can, because it usually means exposing their lives in dangerous quests. If that detail changed, nobody even thought about it yet.

Regarding Lenessia, her combat level is extremely low, because she was nothing but a doll to be married someday, with no power whatsoever.
What has changed though, is that it seems she's got some persuasion/charisma power. Hard to tell if there's a status bar for that. But being able to convince that bunch of free adventurers probably isn't that easy, even if they craved for some fighting, since there's no other reward than doing it.
But since it's only one achievement, and only in a specific context, maybe that Leadership/charisma power is just some silly idea I got