I am a Cognitive Psychologist and spent most of my professional career doing experiments to understand how people perceive and respond to products. The aim was to provide designers and engineers tangible feedback regarding what physical product features most influence perception. I always collected perceptual data using valid psychometric tools as well as physical product metrics provided by engineers. A common finding was that psychometric measurements of visual, auditory, or tactile perception correlated with some, but not all physical metrics. The question, therefore, is not whether subjective or objective measurements are the most valid, but which correlate most highly with one another. You need both. Most important, though, is that you need to know which physical metrics correlate most highly with perception. Don't waste time with physical metrics that don't correlate with perception.
Another interesting finding was that the opinions of designers and engineers often did not align with the perceptions and behavior of the intended users of the product. In healthcare, the FDA requires that medical devices be tested with intended users before it can be certified for sale and use on patients.