I'm curious about what sort of ego issues you've encountered when creating an app. Obviously we're all proud of our idea, but sometimes it can cloud our judgment and make us lose sight of what the goal is--UX and the user journey. Sure, it's important to maintain the brilliance of our initial idea, but also remain flexible for any necessary alterations that may need to be made.
For the UX Designer/researcher, it's not about ego. It's about the results of your user research.* I run into tons of opinions from all the other parties involved - including from the client. The best I can do is say that I observed five people performing this task in a particular way, so the app has to facilitate the completion of that task. Usually people at least give lip service to supporting users, so some of them will see my point.
*Unless you've done no user research; then design is based on opinion and assumption.
In all seriousness, it's an issue in any profession. It is important to remember, you're a cog in a process of your product development, where if you are not in sync with the process (including your target users/audience), you're a bad cog and you can be replaced.
Where there is creativity and team work, there is no space for pride and ego, as I was always told. If you are prideful, you won't learn, progress and you won't become a better designer/teacher/driver/sportsman, etc.
As someone said above, unless you do your job of user research, testing, and analysis of the results, your work will indeed be based on bias and opinions, which makes you a bad UX designer.