I will assure you as a forty year homeowner, that you experience is unique or your perception is wrong, or you are using some awesome hardware I am not familiar with. Valves failing to shut off, the constantly running toilet, is a very, very common failure.I have never had one of the diaphragm valves fail to shut off. The fill time just gets longer and longer and there are, ahem, "occasions" when a 5 minute cycle time on flushes is inadequate.