Okay, I can appreciate that it's driven by gameplay needs, in the case of making a visual language for bandit armor. But I completely agree with Haidrgna. If you have a system for swapping parts and textures of a character, but you only use it on a small, less often encountered subset of the game's enemies, that would be a big waste of the tech!
Use your imagination here. If you have the tech to turn off a bandit's scrap iron chest plate and turn on his bandolier, you have the tech to turn off a farmer zombie's cowboy hat and turn on his trucker cap. Or turn off his prospector beard and turn on his lumberjack beard. Or turn off his fully intact left leg and turn on his gory left leg with exposed bones.
By simply mixing and matching these variants into many possible combinations, you get more variety, more bang for your buck than you could ever achieve by spending the same amount of art time creating whole zombie models that look the same each time. I'd compare it to the variety of randomly assembled worlds compared to the hand-made Navezgane. And again, since zombies are the 'bread and butter' that players see every day, if this variety is worth it for anything, it's worth it for zombies in my opinion.
I should point out you guys have been making some great strides in best utilizing the assets you have, though. Not long ago you changed the makeup of hordes, to avoid multiple instances of the same zombie type where possible. And in 17.3, you made RWG avoid putting copies of the same building next to each other where possible. Changes like these are HUGE for me, because they're smarter ways of utilizing the existing content.