Two Sets of Rules, the Good and Bad?

[Sorinth]

Sorry, "he." Didn't want to assume without a picture.

Anyway, if NPCs with class levels are difficult for you, it's fine for you to avoid it. No one is telling you that you have to use them. But sometimes just plopping a 7th level Diviner with 46 HP into an adventure is simpler than adjusting an MM Mage template to be 7th level and recalculating the CR, which is a nightmare if the spell loadout includes spells like Hypnotic Pattern, Lightning Bolt, Polymorph, Evard's Black Tentacles, and Tasha's Hideous Laughter.

Even if making a 7th level Diviner NPC, there's little reason to build them as a full PC. When you create the stat block for this NPC are you really going to add features like Divination Savant? It's entirely irrelevant for an NPC. Even possibly relevant abilities like Expert Divination which might grant extra spell slots seem rather pointless, it's just work for no reward.