I had a DM/buddy who had a huge 5 subject notebook of NPCs they were basically class X built to 1st, 2nd,3rd, ect ect... some with slightly different weapon or items... and he would mix and match and reflavor them... there had to be 200 characters easy in there. he still found himself just saying "forget this" and just winging monsters/npcs and even then got sick of it.Oh absolutely, I couldn't have DMed 3e if I had kept to that "NPCs must be built like PCs" nonsense. I just gave NPCs whatever stats seemed feasible and explained it as a "Custom Template".
(Note: he also spent 6+ months working an overnight job that in grand total he had to stand up and talk to someone else a hand full of times over the entire night shift... so he was board and made said notebook)