Re: Shift kit and deraileur gears
I'm on my second year of my shifter kit with my same gear cluster cassette and no bend/missing teeth. I shift hard all the time - in an attempt to break stuff. I think the key may indeed be the quality of the stock gears, but chain tension and derailleur setting are very important as well.
People have broken and bent weak axles, one or two have broken derailleurs but I can't remember anyone tearing teeth like other than the time the guy (who never rode a motorized bicycle at all before) somehow crashed Jim's bike.