To me, if you get an idol that wasn't damaged in collection and transit, it probably will eat and eat a real variety of foods aggressively. I don't think that is necessarily the case with copperbands. Maybe it just takes less to injure them, but many will starve themselves to death or just up and die after eating for a while and they tend not to be aggressive eaters or interested in a great variety of foods.
I agree that origin plays a large role. Cbbs from Australia seem to do very well. It may be that the sourcing of idols has improved dramatically (more from Hawaii and the near Pacific islands, less from the Infdonesia and Philippines areas??).