American "Cross-over" Singers - Should History Continue to Shun Them?

It seems to me that a certain group of performers has pretty much been relegated to a lower rung  on the historical ladder, and perhaps these singular talents should be brought back into the field of recognition they deserve.
I will mention but a few at this time, concentrating on the male singers, with  intentions to deal with the ladies who belong to this group, at another time:
The names of James Melton, John Charles Thomas, Richard Crooks, Robert Merill and Jan Peerce appear on my mental blackboard at this moment, probably because they were part of my young years as a listener.
The primary reason for my bringing these names into focus is that they were performers who possessed wonderful voices, and  who sang both popular and serious music, achieving  considerable recognition and stature in both aspects of music. For the most part, these performers attained equal  distinction in, say, Broadway music and Grand opera.  To cite examples of reality about their gifts, one might sing an Irving Berlin tune on one radio broadcast, then be heard singing under Toscanini on another broadcast performing  Italian Opera. I know, for instance,  that John Charles Thomas would sing "Danny Boy" on a particular evening, then be heard with, arguably, the greatest Russian singer of the time, Feodor Chaliapin, just days later, in Grand Opera.
There are others I am not mentioning in this blog, be assured. It was a period, in the twentieth century, of some really glorious singing cloaked in  a wide view of opposing forms of musical styles.  I'm sure you can find  examples on your computer, and become witness to an engrossing period in the history of musical performance.