But, you do realize that this cannot possibly be argued as objectively making the setting worse, because that is a matter of preference. Do I agree with you? Yes, I do, in fact, agree with your contention that Forgotten Realms has been made worse over time. I entered the game in 4E, as I am too young to have entered much earlier, and, I was so dissuaded from playing the setting by internet dwellers complaining about changes to the setting, that I did not play FR until I began playing 5E. I do not wish to imagine having one of my favorite settings, say, Eberron, be destroyed by careless inclusions.
However, this all comes down to preference, which is why you cannot prove that the setting was made worse. Do we all know that the setting was made worse? Yes, intuitively, many of us do. But, there will always be those who insist on evidence, even when it is in the field of subjectivity.