See I've heard and talked to the best in the world...(I have friends that call competively. I don't feel the need to name drop)...and most I know carry several diaphrams and other calls in the field and even switch during contests to sound like more than one elk due tonal restrictions. Sure you can change octives, pitch, and volume but even by changing the shape of your mouth, using your hands to deflect, changing locations of the call in your mouth (this is why I don't like the Primos dome) and even using your voice behind it you still sound pretty much like one elk. Especially when cow calling granted one elk making lots of different sounds.

I think that mastering a diaphram is important but saying that one call with do it all might be limiting you more than you think. Don't let your ego get in the way.

In the end I think we'll just have to agree to disagree. In short some feel one diaphram will be all you ever need and others feel that several calls bring better success by using different calls in different situations.