Problem is, someone out there may not find that monotonous, while thry find something even simpler to be the threshold for monotony. Someone may argue, how many measures does something need to repeat in order to officially qualify as repetitive. It may repeat, but how much exactly must it do so to qualify for that descriptor on a technical plane. They have BPM, meter, or Adagio markings, but someone may consider 4/4 fast, while another finds it the slowest thing since retarded tortoises. Although you may be right on speed, as it has actual numerical quantifications. Nonetheless, speed, or descriptors like "fast" or "slow" are already opinions and subjectively loaded from the beginning. Someone may regard Mach 2 as slow, but Mach 13 as fast, or Mach 1 as fast and the speed of sound as slow.