It is especially difficult for professional service firms, including creative agencies, to distinguish much less differentiate themselves.
Your Positioning may inform the development of your Competitive Advantage, but your Competitive Advantage will determine your actual Position.
I find David C. Baker’s thinking on leading and managing creative service businesses, and professional services businesses, exceptionally relevant, direct, and applicable. Sometimes it is most effective to define something by what it is not as much as by what it is.
In this article about competitive advantage, David does both: https://www.recourses.com/agency-moat-sustainable-competitive-advantage