"Full stack" is useless in the same way that "Agile" is useless. Specifically, it's useless because it was hopelessly cargo-culted and overused due to the original power of the idea.
5-10 years ago a full-stack developer was a very meaningful distinction. Today, every hacker wannabe Uber driver that went to a dev bootcamp for 3 months calls themselves a full-stack developer. "DevOps" avoids this fate only because the subject matter is slightly heavier and harder to fake.