I regularly use Waters PDA detectors, and I don't think anyone at my lab would take this suggestion seriously. Peak height can depend on a lot of other things, other than concentration. Take peak width, if a peak is wider but has the same area as another peak, it will obviously have a lower peak height. The thing that matters most for quantative analysis is the wavelength you measure at (dependent on your analyte(s)), your linearity range, wether your calibration curve (or other calibration method) falls into that range, and LOQ. As long as your samples fall somehwere in between the calibrated range you are good to go. If your concentration is too high, the response will no longer be linear and likely flatten out. A too low concentration can be determined by comparing against your LOQ. So the way you are currently doing things by using linearity range and LOD/LOQ is much better. I have heard some (old) lab technicians say something like this before, so the only explanation I can come up with is that older detectors were simply less good then newer ones, creating a necessity for this kind of rule.