The closer he got to his real self, the more he panicked. Finally, he was let go and another voice was called to do the spot. The smaller the market in which you work, the more versatile you need to be to be super successful. This doesn't mean that if you don't do a gazillion voices along with your straight reads you're not going to work. If you're good, you're going to get work.
Some people only do hard sells, and they make money.
They'll make money too. There's no way you can clearly show all the facets of your delivery skills in 60 seconds. You're only going to use pieces of each commercial, any way. Don't use full spots. A demo tape is a sample, not an encyclopedia.