Henry
Autoexreginated
Problem is, your bug is my feature, so the answers are going to differ widely depending on how one sees it. Having NPC use the same back-end mechanics as PCs used to drive me crazy in 3e, 3.5, and Pathfinder because they had dozens of stats I didn’t need for someone who was going to last for one or two sessions and get killed- or worse, five minutes and get splattered. AD&D didn’t require it (many adventures had poisons invented for a single scenario, villains who had powers that weren’t in any class features, etc) which is why I was glad when 5e built In ways around it.You've pointed out this glaring example of bad design in 5e a few times now.
The OP, I think, is looking for ways to overcome this bad design so as to maintain some internal consistency in his/her setting while at the same time being able to run the adventure s/he wants to.
Got any suggestions?
However, sounds like Helldritch has found a solution, so all is well.