If a house has no unbalanced issues for 12-15 years with copper and the valves don't change, only the piping changes, & the owners don't change their habits, yet notice the flow irregularities immediately... well, draw your own conclusions. No modern mixing valves involved anyway, just simple on/off, old -school style. Different clients telling the same stories, and keep in mind Florida has an scourge of re-piped homes. Dom.