Well, thank you for asking. 🙂 What follows is my own theory about why single-coil pickups have a greater dynamics range and thus forces you to develop better control over your dynamics. I’m not an expert on electric engineering — so correct me if I’m wrong anywhere.
Traditional single-coil pickups have weaker outputs, probably weaker than most, if not all, type of magnetic pickups. With most electric guitar amps, there is a threshold of distortion — when the input signal is stronger/louder than a certain level, the sound starts to distort. And you know what happens when the signal reaches the distortion point: instead of getting louder, it distorts. Which is a good thing when you’re playing rock music. Not as good, if you want to develop a good picking dynamics.
When the input signal is weak by default, then there is a greater range between the weakest input level and the point of distortion:
With high-output pickups, like many of the modern humbuckers, the default output level is much hotter. This results in a reduced range:
When you practice on high-output pickups all the time, it becomes harder to develop one of the most powerful tools in musical expression — dynamics. The difference between soft and loud. If you were playing classical music, this is not good at all, as classical music demands that you develop a good control over dynamics. A master of instrument can produce good tone across the whole range — from the quietest to loudest, and is able to play at any loudness at any given point.
But popular music is a style where we kill dynamic range. Recordings we hear are compressed — there really isn’t much difference in actual volume between the quietest and loudest part. This is so that you can hear all parts clearly over background noise (like in a car or airplane) and the whole thing gives a “loud” impression, even when it isn’t actually. This is neither good nor bad, I’m just stating the facts.
That said, if you want to become an expressive guitarist, dynamics is a range that you’d hate to ignore. Practicing on high-output pickup makes it harder for you to develop good picking dynamics, whereby your technique is quite rough but when played through highly distorted amp/tone you just can’t hear that level of details. On a mildly overdriven tone, you can use picking dynamics to control the amount of dirt on each note, giving each note more expressive characters.
Simply put, if you want to develop this control over picking dynamics, single-coil pickups are better at forcing you to do so. Then, when you’re performing, you can turn on your dirt pedals and switch to higher-output pickups. It feels easier to play, and little imperfections in dynamics will get covered up — more forgiving and thus more cohesive performance.
And final rant: popular music’s disregard for dynamics is one of my pet peeves. It is the root cause of the current Loudness War in mastering and much creative opportunity is lost as the result. How can you make loud and heavy parts feel that way, if you were robbed the ability to contrast it with soft and quiet parts? I love heavy music and I want my pounding and thrashing to hit my audience with full impact. I am not saying pop music has to be the same as classical, but I do want to retain my dynamic range. Thank you very much. 🙂