I am a Full Stack & DevOps Engineer. Jack of All trades, master of none, certainly better than master of one - At least as far as nascent startups are considered. I Architect, design and implement front-end, backend and mobile applications. I also Deploy and manage the servers. Just enough stuff to get the product of the ground and get it running on production (an MVP). After that, people hire specialists as required to build upon it.
Hiring many specialist is a luxury that a nascent startups with limited capital cannot afford. Full Stack best suits those situations. But as the company grows, it should opt for specialists.