I really am struggling to believe that properly made sprockets could be deformed under pedaling loads, although i'm no engineer. Are the teeth bending or the whole cog deforming? Have you got a pic? If it's deforming side to side then surely there must be some movement somewhere in the system? If the teeth are splaying out it suggests to me that the chain is getting on the wrong side of some of the teeth and bending them. Had that happen on a chainring when i left a bolt off and snapped off a tooth. Hard to see how it could happen on a sprocket, bent axle or something like that.
