Tithonus

I would say in terms of cracks in the spirit web, you've essentially got a big enough hole to let the rest of the investiture flood in. That'd explain why some mistborn are weaker than others, but I'm not how it makes sense in the context of hemalurgic spikes. I'm fairly sure BS said they're of a more spirit realm-y thing and above there's some quote about it working the same way as the souls of dead bodies so I'd say the spike is like a separate conduit for power like how mitochondria has different DNA. I know BS has a degree in biology so it's not like it's a reach to say he could've thought of that.