Yeah, that was another issue I had with the APs I've played. We played the 3.5 Rise of the Runelords and some of the encounters there were fine, but some of them would have blown away casual players and one of them did blow us away (TPK) even though we've played for 20+ years. Same thing in Serpent's Skull (although our GM was very good about making allowances that at least gave us a chance).
The end boss of Kingmaker is a case in point. AC 51. Huh?