great musicians always enjoy practicing- it is like making something new when done properly. If they arent enjoying it, they know they must get creative about it— otherwise it’s mindless.
True, though I'd still say the individual day-to-day practices can sometimes become dull. As you mention, this is where I think a lot of "fun" activities form - experts looking to spice up a particular activity. I like to train some kata by going as slow and precise as possible, then as fast and reckless as possible, THEN settling for normal speed.