It’s fairly trivial to present NPCs as being fictionally consistent with PCs even if they have different mechanical underpinnings, unless the players are actively looking at the NPCs mechanics and trying to confirm that they match PC build parameters.
What aids me in this is that I’m a stickler about presenting every NPC as unique, and being very clear that classes are not something that’s extant in the fiction. A PC and an NPC might both call themselves “wizards” and use arcane magic, but they learned magic differently and have different talents, and this use very different mechanics.