There are a number differences of having Breslov with Nanach as opposed to assuming Nanach is not needed. Here is one of them.
Often people that have Breslov without Nanach use it as a personal tool for self growth. For example they will try to be happy, holy, reach higher levels, gain knowledge and understanding etc. through the teachings. However it is often on a personal and selfish level.
By contrast with Nanach it is all about the Tzadik, about living attached to Rebbe Nachman, about breathing Rebbe Nachman, about using every ounce of our energy to spread Rebbe Nachman.