I think we may have different definitions of what significant power means. I managed to break the metal rod inside my plastic pedals one time… But yeah, I used an 8 speed hub gear with a toothed belt for ~7 years, which I don't see breaking any time soon. (Though I did have to walk home a few times due to other reasons, e.g. clogging the gears up with snow or flat tires.) But it doesn't switch gears when under power, and if you start giving power while it hasn't fully switched yet, it makes very unhealthy sounds.