I hereby stipulate some of the best music I have ever heard (Miles at the Blackhawk, Bye Bye, Blackbird for example) slows down like a MOFO and swings every minute while going down in tempo.
I sure wouldn’t be suggesting that Jimmy Cobb and Paul Chambers and the rest of the band be putting in extra metronome work.
I frame it this way…the goal of playing with the metronome is NOT to learn to play metronomically. It’s simply a listening exercise.
As in “are you able to listen to TIME that exists outside of yourself and play WITH it?”
In that respect, it is the perfect exercise/discipline for students to practice.
In fact, if one can’t play well with a perfectly predictable machine, there would be serious doubt as to whether that person could play well with humans, who as we all know, are never perfect.