Whether you play to speakers or headphones, if you are playing to a recorded track, you're following. The only way to truly lead is playing with live musicians and no backing tracks. Even if I'm playing to a click...I'm following. I can't lead the click.
I like speakers too because you can work on your drum dynamics in relation to the speaker volume, good real life training IMO.
I get what you're saying, but I'll try to clarify below.
How would the playback medium change how you play to it?
It was over 20 years ago, so my memory has faded a bit, but if I recall correctly his rationale was that playing to headphones becomes a crutch (even if you turn your headphones down) because you don't "meet the music halfway" while playing as you do in most live situations. When you play to headphones, it's easier to anticipate what you're hearing and react to it, as opposed to playing to speakers which is harder to react to.
The difference in reaction times may be small, but he thought it was enough to make the difference between dragging ever so slightly and grooving - hence why I used the words "follow" and "lead".
When it came to this teacher, I eventually trusted myself to defer to what he was teaching and showing me, even if I didn't necessarily believe what he was saying, because, simply put, his playing was
that good.
Regardless, I know that I find it much easier playing with headphones on (even on low volume) than I do playing to speakers (even on high volume).
Maybe what beatdat was trying to say?
I've heard that playing to the speakers helps you keep your volume level with what you're playing without ear plugs, like you would with your band. Isolating your hearing from yourself with noise cancelling phones allows you to play louder than would be appropriate in a group situation, without realizing it.
Playing dynamics appropriately was more a result of learning to play to speakers, but the purpose of playing to speakers was to improve my timing.
When I've played with "speakers", I've had to turn it up so much to hear it correctly
For sure, that happened to me when I first tried it, and for sure it was a lot of work learning to play to speakers without having them so loud that it drowned out what I was playing.