touchy subject….hard to explain…. when pup R start to approximate amplifier input R (Z) these dimming effects become more prominent…traditionally, amplifier input Zs are in the order of 10kOhm…TBird pups approach that value…mainly the reason low Z pups are so popular for recording….
with hi R (Z) pups even cable lengths can play a role….active electronics somewhat address these issues at the expense of on board batts and latency (not a fan)…this said, an active setup is much more predictable than a passive one because they can be linearly scaled as opposed to a passive setup where the knobs “do something” that can’t really be quantified to the point one can intuitively and consistently rely on numbers on volume and tone knobs…