Yes, this is a very confusing condition, that almost defies understanding...because there seem to be a host of varying symptoms, that affect everyone differently. Not to mention, there may be multiple causes.
Certainly, there seems to be an "acidity" connection for some people, and those with normal GER can trace their temporary symptoms to something they ate that caused an overproduction of stomach acid. But this is not always true with GERD. I don't dispute that there are some that have a perpetual overproduction of acid, and I think for this subcategory of patients, the diet can probably offer some relief. Perhaps some of these patients have a normal LES, and the symptoms are due to "normal" reflux that carries a larger-than-normal amount of stomach contents/acid with it. So, if the acid is managed through diet, then the normal reflux won't be as corrosive.
Then, there are the vast majority of patients (IMO) with LES issues, either by way of involuntary muscle problems, or abnormal nerve signals via the vagus nerve. For these folks, perhaps the only diet adjustment that will offer much is eliminating trigger foods.