Broadway performers are the only ones who are asked to sing in separate register qualities on purpose. Classical singers must generate resonances to carry over accompaniment without electronic amplification. Singers of other styles just sing however they do.
Broadway dancers must be able to do ballet, tap, jazz/modern, and sometimes other styles. Actors might be in a Broadway show at night and do commercials during the day. The specialization in theater is generalization.
Training anyone to do just one thing at the level of mastery takes a long time. Ten years seems to be what it takes to be at an elite level at anything….golf, tennis, dance, music, singing, acting. There are reaons why there are very very few top experts who are good at more than one art, sport or skill. People who cross over often don’t do too well, as they just can’t fake having skills on the other side of the fence that are equal to the ones they have at home. Wynton Marsalis plays mean jazz and very good classical music. I believe Andre Previn plays both classical and jazz piano. Trying to think of other examples is difficult. Most of the folks who have successfully switched genres have done so by quitting one and going permanently over to another.
Why is this important? Because the people who deliberately cross train, like atheletes in the triatholon or decathalon, or the Iron Man/Woman Races, train in several ways, not just one. And, they do not complete against the atheletes who are specialists in only one of the sports they do. They can’t. For singers, if you want to try to be a high belter, you can do that, as long as you work with someone who understands how that happens, but you CANNOT also sing difficult classical music at the same time and do it really well. You might be a really great country singer, but that isn’t going to help you do a Broadway show like “Show Boat”, no matter how well you sing, as the vocal skills are very different. And you might be a terrific opera singer but that isn’t going to help you sing “Tits and Ass” from A Chorus Line.
Training needs to be specific to the task. Each of the CCM styles requires the vocal apparatus to be used in a unique manner, albeit from a chest register (speech) driven place. The confusion about making the “right” sounds has to do with understanding what type of default production is necessary in that sound and how close or far away any given singer’s throat is from making that sound naturally (or easily, if it is learned).