Part of the problem is I am so connected to the D&D world that when I'm reading these books I'm thinking of them in game terms. Wrong thing to do, I know-
Back in the 2e-4e days it TSR/WotC occasionally would publish (usually in Dragon Magazine) stat blocks for characters in the novels. And of course there are the Heroes Lorebook, Villains Lorebook, etc. sourcebooks that do the same.
And Elaine Cunningham has said that when Jeff Grubb was overseeing things in the late '80s through mid-'90s, it was routine to check the events of the novels against what a PC or NPC with that class, level, items etc. would be capable of! Writers could, essentially, fudge the rolls for characters, but they couldn't have characters accomplish things they wouldn't be capable of in a game session.