Suppose you're developing your own app or say any product. Is it really possible for you to grow your product despite having your own unique idea and targeted audience? Don't you think a big company which have solid developers and coders in their company with its own user base can trail you far far behind just by watching out for your idea and executing it with exceptional quality?
To me it will probably vary on a case by case basis. Mostly, the only answer in one of those cases comes from trying to execute and seeing what happens.
Good luck.