Good post, but I have a quibble. Whether or not an NPC uses the same rules as a PC impacts consistency, but I dispute in impacts verisimilitude.
A baker with a +10 in cooking utensils must be a retired adventurer impacts verisimilitude more than recognizing that an NPC that isn’t an adventurer is better at non-adventurer things than a dungeon crawler.
Also, the fact that certain features just aren’t available to PCs also doesn’t impact verisimilitude: after all, the players can’t play monsters either.