I get the basics inside material editor, that's the great with Corona's rendere mat preview. It's not super accurate because it has weird large Area lights that make gauging proper glossiness very hard but, it does the job well.
But then I test the material in real-conditions, where I intend to use it in scene, or item I plan to use it on. Because you don't know if your material behaves like it should unless it's in proper, controlled environment.
For example, my most complicated material was Corten or rusty steel. I had like 10 photographies of how it was used in space I recreated and it always behaved differently, with sun, no sun, interior, exterior. So I always did a short series of test renders in every condition to see if the behaviour matched. Artificial material scene would not tell me that.
Regarding the Disney's parameter amount, I think they simply wanted faster control over layered speculars (tint, thin film, sheen,etc..) without the need to manually create this layers as Blend material. If you use them, you have them exposed, if you don't need them, don't touch it. But it's there, easy to use directly with 0-1 artistic control. Easy to understand, flexible to work with. No, it's not for Cartoons :- ) The stylization or style, doesn't matter.
