It depends on the goal of the new language. If the goal is to break away from the other language and present a better one, it's a noble goal. Although, if the language isn't adopted the goal might not be fully met. On the other hand, if the goal is to get more people to use it then your logic would be correct. This was the case in the development of Modern English given the diverse amount of native speakers(the language became a Kluge).
To answer the question you have to look at the usage and satisfaction of a sign language that went that route from a native perspective. You need the native perspective to see if it meets the majority of user needs(English is far from perfect, but fits the needs). On here, the majority of people(who post, or are the loudest) use ASL. Because of the amount ASL users this forum might not be the best place for answers to your original post.
