There may be plenty of quibbles about just how tough an NPC should be compared to an up-and-coming PC, but I think it's understandable and fair for them to pick up a little on-paper combat (combat survival) ability along the way to picking up more formidable and important abilities as they gain life's experience. As long as they are then equipped and played in appropriate character, they'll put up the fight they should put up (which may be not much of a fight).
Actually this is one of the common dissonances of games with levels. Power is attached to level, so a high level whatever is always better than a low level anything.
The best tailor in the world can defeat a platoon of militia. Also, he can defeat an ogre. While this is cool and fun in some instances (like Mickey Mouse's Valiant Little Taylor or whatever), it does make a dissonance with the game simulation. It's a minor one (because unless your game goes around taylors battling monsters, this won't happen in 99.99% of the cases), but it's there.
I also find it weird in the opposite sense. My fighter is pouring points into blacksmithing. In order to finish a masterwork plate, I need a couple of extra ranks. So I go to the nearest hill, start to kill goblins, and then I'll be able to craft it.
I don't care about it, honestly. It's part of the game. It's the necessary evil behind the level system, which I think it's the right one for games like D&D, where players are heroes that start fighting goblins, and end fighting Dragons. It also models right the typical NPC: Galadriel should be harder to poison than your average dwarven grunt, not because she has higher CON, but because she has higher level. That's what I want the system to express, and I can deal with high level artisans and crafters being somewhat bad reprersented, if that's the price.
EDIT:Maybe 5e bounded accuracy is a good step to solve this minor nitpick, though.