I thought that was a silly discussion (sorry). With absolutely no constraints, there would be no styles, and in fact no music. Music is about recognising some patterns in sound, so there will always be some constraint in there.

Um, no. That wasn't the point.

One point was that was an arbitrary constraint like serialism isn't particularly interesting, and certainly no more inspiring than any other arbitrary constraint.

Another was that before serialism constraints were based on musical experience, not on playing with numbers. There was no reason not to continue in that direction - which is what eventually happened anyway.

Another was that it was a deliberate attempt to invent a new musical language for the sake of it, and as a deliberate attempt it had very little of interest to say. Artistic languages evolve organically, blending all kinds of influences. When that isn't the starting point, there's no delight and few surprises.

And also - serialism was mostly a political statement about the politics of composition and the exclusive status of the composer and the 'educated' listener. The sound was a footnote to the sociology.

These are all reasons why styles are not the same as constraints. Styles are organic things composers grow up listening to, copying and riffing off. Constraints are deliberate and conscious intellectual games which sometimes help with good music, and sometimes don't.