How can sound be used in any powerful way without being able to control it to produce specific changes for the better? And how can one even know what DNA changes are needed? Are there certain positive frequencies that correct accumulated defects?

You were circling around the essence of the problem here, that with the intuitive awareness that sound has healing characteristics, the problem then becomes what can truly be influenced by a sound manipulation and what might not be, and then, the issue of what kind of sound is needed, its characteristics, the type of delivery, and then, what vibrational frequencies, and for how long, and with what degree of repetition, to perhaps have a series of treatments, and so on. There is an infinite variety, in fact, of such stimuli that could be experimented with, but there is insufficient time to explore the almost endless series of variables, not only in the nature of the sound therapy and its delivery, but what outcomes are most suited to benefit and how best to go about testing that, in all the various details of the research plan and protocol making it quite complex and unlikely to be done in a serious and extensive enough way to make progress quickly. But there are potentially great benefits given enough time to pursue this. What we see is that with the short-term timeline available to humanity, one way or another, this will become a relic of history once you leave the physical plane altogether, and thus is a partial measure that will be unneeded for humanity in the future.